Anyone else have this problem? Bill for 2-year contract went up after 1 year

On 6/22/19 I started an Internet Plus Basic plan with this in the confirmation email:

After taxes and fees:

My bill was pretty consistent around $69/month, then rose in July quoting a new price $59.99 for the Internet Plus Basic plan.

I've chatted and talked with customer service, both times they confirmed that my contract should have kept the $49.99 price for 24 months but a "glitch in our system and the discounts of the packages were removed even if they are still under promotion. We are starting to fix the issue now" (this was in early August) but I continue to get higher bills. When I called at the end of August, they still had no ETA for the fix.

I have been paying my regular amount instead of the higher amount because I am on a fixed income and I should not have to pay the higher amount due to Comcast's billing error. However now I am getting threatening notices that since I have balance due (the amount of the error) they will turn off my service next month.

The agent on the phone said I should pay the full amount of the higher bills and trust that they will refund me the incorrect amounts later when the glitch is fixed. Ha! I cannot just afford to pay more for somebody else's billing error.

It seems unusual for billing error that causes over-billing to remain unfixed for 3 months (at least). In the meantime, we have no choice but to pay for their error and they have no motivation to fix since they are just getting more revenue. If enough people are experiencing this, do we need to bring a class action lawsuit to force them to fix this?