discount on internet bill for having xfinity mobile never applied automatically

On March 20, 2023, I contracted mobile telephone service with the company Xfinity Mobile, within the framework of a current promotion in which contracting the unlimited service agreed to the purchase of a discounted telephone, to be paid in 24 installments, and a once the line is activated, a usd 20 discount will be applied to the internet bill for 24 months as well. To obtain this promotion, I contacted by telephone and by the company's chat to confirm that this promotion of the telephone and the discount on the internet bill corresponded to our account. The service was activated on March 23, and from the first day I contacted them to see when said discount would be reflected on the internet bill. Their answers were that it would be seen automatically, but the following months when it was not applied automatically, the same representatives of the company applied the discount manually. Escalations were made for which they always said that it was going to be solved. They believed that it was a service problem since in January a chip had been requested that could never be activated but for them it already appeared as an existing number, but that would be solved.
The bills for the months of April, May, June and July had the discount applied manually. At the end of June, I communicated to be able to finally resolve this inconvenience, since I am claiming from the first day the service was activated and they inform me that there was actually a confusion and said discount does not correspond since the service had been applied to the first hiring in the month of January (which could not be activated). The only solution they offer me is to add another person to the line or change the phone number to get the bill discount but having to pay off the phone debt, thus losing the possibility of paying for the device in installments. I try to explain that both in writing and by phone they had told me that this discount corresponded to me and that since the first month I have been trying to solve it and they not only do not solve it but to obtain the benefit the only harm is me, for having to spend more money by adding one more telephone line or by changing the telephone number, with the problems that this can generate and also losing the possibility of payment in installments.