Autopay discount

When I signed my Comcast Business contract, I was told I'd get a $10 discount for choosing ebilling and autopay. I opted in for both, added my business debit as the default payment simply because my card was handy, and then didn't think anything further about it until I realized there was no discount on my first bill. In the meantime I changed the default payment to my business checking - but now when I inquired about the discount, a chat representative told me I can't get it since I initially used the debit card. Is that correct?? I used it literally one time and then switched to checking, and I'm no longer eligible for the $10 credit going forward? Can someone in customer service please help?