Billing is messed up

After many runarounds with tech support not being able to enable what I needed on my cable modem, I finally installed my own and returned the Comcast modem. That was in February. Now it is May and I'm STILL getting billed for the equipment charges for this equipment that I returned months ago.

Last night I called someone at Comcast who made a note of it but said they didn't have the power to fix the billing. He forwarded me to some other number that kept me on hold for 10 minutes while nothing happened except music playing. Finally I hung up.

You have my information, you know that there is a billing issue, and you have the related information. Please fix this. Take the charges off my account and apply a credit going back to February. I do not want to keep getting bounced from one incompetent person to the next and being stuck on hold waiting for someone to correct the billing.