Tryinng to get CenturyLink to repair our interent. Need advice/help.

[SNR_]

This is written in long form to preserve details.

4 years ago we purchased, for the business, from the only cable-based internet provider in our area an 8Mb/s connection over ADSL from CenturyLink. Over the years we have had problems with our internet either losing the connection, or the speeds dropping down as low as 3Mb/s. The time before last that a tech showed up, he worked on the connection, said he had done all that he could for us, and we started to get 10Mb/s, which is impressive taking into account the distance. This most recent time the service tech showed up and diagnosed CL's cable as failing to preform to specifications. He said that 1 pair was throwing too many errors for 8Mb/s and the others were, as he put it, "dead". He said that they needed to install a new cable.
Now I have heard from other internet techs in my lifetime that the internet cables need to be replaced every 2 years to maintain maximum speeds. IDK how true this is.
We recently got a mailing indicating that we are getting a new contract with CL for 6Mb/s internet and phone service, which we never had nor did we order. Moreover, they're planning to charge us $300 for running the phone cable!
Naturally, we called them up using the cellphone, only "the call couldn't be completed as dialed". Tried again and again with the same result. Tried with wife's phone, which CL also knows about with the same result. Borrowed a phone from someone else and got through, no problem. Is CL blocking my and the wife's number?! Concerning the downgraded speed, CL rep said that she couldn't give us more than 3Mb/s, what we were getting on one of the bad pairs, so we should be happy that we are going to receive 6Mb/s. The person on the other end said that we were not receiving any phone service, but couldn't explain the charges on the sheet, which is the planned bill for this month, for phone service, 911 service, etc. We asked to speak to a supervisor, and was told that "the supervisor would call us back today." Still waiting on that.

So how do we get CL to hold up their end of the contract for 8Mb/s? How do we get a replacement cable? Is there anything else we should be aware of or can do?

Thanks!

[SNR_]

PS: Unless I misunderstand, much like with any other business connection, this is not an "up to" speed, but rather a contractual guaranteed speed.

[SNR_]

Update: After looking over our original service agreement, it appears that they have an internal phone number connected to our account hence the strange phone number and 911 charge included in the bill. It remains unclear why they have to do that.

[Philip]

ADSL speeds are "Up to", rather than contractual guaranteed dedicated feeds.
Phone numbers have some mandatory 911 fees attached to them, including phones using VoIP that require internet service to run. I am not sure what you mean by "they have an internal phone number".
Cables should not need to be replaced for many years if they're the correct type, i.e. rated for underground, or UV protected for outdoor use, etc.

If your copper phone lines are degraded, the service will be very slow and there is little you can do, short of replacing the line, using a different pair, or finding the culprit/faulty connectors.

[SNR_]

Update:
We've spent +4 hours on the phone across several days with CenturyLink.

Eventually, we've learned that they stopped selling our original 8Mb plan. They now sell a 10Mb plan and told us they could only downgrade us to the next lower plan which was a 3Mb plan. I'll post more details in the quotes below...

ADSL speeds are "Up to", rather than contractual guaranteed dedicated feeds.

We successfully got CL to sell us a 10Mb plan along with a new cable, but then an internal team canceled the order. I asked why, and CL said that they can't get that speed to our property. In other words, they're saying that the business plans are not "up to" speeds like "consumer" plans. Again, this is not my opinion, they literally told it to me personally.

Phone numbers have some mandatory 911 fees attached to them, including phones using VoIP that require internet service to run. I am not sure what you mean by "they have an internal phone number".

Those were not my words, that's what the CL rep said. We never asked for, nor received a VOIP or any other phone service here.

Cables should not need to be replaced for many years if they're the correct type, i.e. rated for underground, or UV protected for outdoor use, etc.

Their cable is multistrand and black in color. I guess I could dig it up and read the ratings off of it... then again, maybe I should leave it alone.
If it's the same type of underground multi-strand cable as my father has worked with for years, then it has only fair water resistance.

If your copper phone lines are degraded, the service will be very slow and there is little you can do, short of replacing the line, using a different pair, or finding the culprit/faulty connectors.

So far the techs have been swapping out the pairs. This has been going on for years, only now did they finally run out of good quality pairs.