Inconsistent information of mobile plan

I previously had an Xfinity Mobile line under an account where I was not the primary account holder.

Before starting a new Xfinity Internet service, I called to confirm whether I would still qualify for the $10 Unlimited Premium line promotion, even though I had used Xfinity Mobile before. The representative confirmed that the promotion could be applied. When I transferred my number to the new account, another representative confirmed the same.

However, I am now being charged $50 before tax each month. I contacted Xfinity Assistant and was told the promotion could not be applied. I then called customer service, and they again confirmed my eligibility, issued a $40 credit for the first month, and said my rate would be adjusted going forward.

The adjustment never happened. I was later told I would need to call every month to request the credit, but I still have not received the latest credit. I do not think it is reasonable to call every month for an issue that should be fixed permanently.

Could someone please help apply the correct promotion and issue any missing credits?