Smartwatch Promotional Credit

I purchased a watch as part of the Xfinity Rewards $300 promotional credit. Upon activation, customer service attached the watch to my wife's number without my approval. Upon fixing the issue, the Customer Service rep had to deactivate the line and add a new one, effectively cancelling the promotional credit, since the "old" watch line is deactivated. I did not realize that was going to happen, and there was no warning from the rep that was going to happen. Two months have passed, and Customer service has credited me the $12.49 credit for the watch, but they should be able to credit me the $300 in full minus the $12.49 from the previous two months.