All CC systems were supposed to start charging cablecards as a A/O fee, BUT then you're supposed to get a "customer owned equipment" credit, which varies by market. You can find this credit out here:
»www.comcast.com/equipmen ··· ect=true
In your market it appears to be $2.50 (same as my area)
It sounds like you were NOT being charged the A/O like most others were all along - so you are now being billed the way you should have all along.
Actually, it really sounds like they were charging your CC's at the rate they charge for a 2nd CC in the SAME device. (some older Tivo's required a 2nd CC)
»customer.comcast.com/hel ··· ablecard
If you have a CC on your primary outlet, then you'd still get a credit on it as well.