HUGE Billing mistake

Comcast made a HUGE billing mistake on my account. I caught the mistake after about 6 months and brought it to their attention. Instead of fixing the billing moving forward and thanking me for catching that, they back billed me almost $10,000!! I was told---"you are getting 2 months free". Well that was only because they did not have the ability to back bill be more! If I would have just left it and not pointed it out, I would have continued to be receiving the discounted billing. I think this is totally unfair. I should be thanked and maybe billed 1 month previous instead of being slapped with a $10,000 lump sum bill!!

No one will help me and I was told to fill out a complaint form online for someone name Tom Karinshack. Well guess what---I can't find anything about that!