Being charged for both Residential internet and Business internet

In Oct of 2024, I contacted Comcast Residential sales and asked to be switched from business internet to residential internet.  They told me they had done this and my business account was closed and I would not be charged any longer for the business connection.  I got a new cable modem in the mail, activated it with Comcast support, and that was supposed to be that.

Instead, both are still open to this day and I'm being charged for both.

I contacted business support and asked for a refund for the over $3000 I am owed for this negligence, and they refused and said they had no record of me asking for my business line to be disconnected.

What do I do from here?  I am *still* being double charged by the way the support rep did not fix that for me.

I asked the support rep why would I open a Residential line last year and then keep my business line but not use it.  He said sometimes people want two lines, which I do not believe is even possible with the physical wiring to my building.

I asked to speak with his manager to explain how this was not really satisfactory and he refused saying there was nothing else that could be done, since there was "no record of me asking for the business line to be disconnected".

Now I am very confused and don't know how to proceed.  First I would like a refund for 7 months of double payments, but more importantly I'd like the Business account closed and to not charge me any more in the future!  I also want to do this without interrupting my Residential service.

How should I proceed?