Complaint Review: Cox Communications

Alarmed at the rapid increase of my monthly TV service, I called Cox Communication on 3/19/13 to see what I could do to lower my bill. This is when I found out that in fact, for about 15 months (since December 2011), Cox Communications has bumped up the number of my TV receivers and remotes from 2 to 4 on paper! I only have 2 TVs, so there was really no need for 4 boxes.

When Cox's rep realized this, he offered to give me a "generous" credit of $100 when in fact the surcharge is really worth $203.70. Their explanation is that I noticed the mistake too late and did not report it, which makes it my mistake as well. They cover themselves with a note on one of the last pages in their statement saying : "If you have any questions regarding your bill or disagree with any portion of your bill, immediately contact Cox with your concerns. You must contact us no later than 60 days from the bill's due date..." 

Does this sentence give them the right to keep the money that is not rightfully theirs, even if demonstrated that they are wrong? No note says that if more time has passed, they will not reimburse the overcharges resulting from their mistakes.

 How could they not know that I only had 2 boxes? Don't they keep an inventory of their boxes? I am sure this mistake was done on purpose just to extort more money for nothing and I am outraged!!! Isn't it interesting that they never err on the part of the customer, but always in their favor, which tells me something: this was no mistake!

Please help! I would like to get back the rest of the money I overpaid for their "honest mistake".  Do I have any recourse in this matter? Thank you in advance for your help.