Happy Thursday, magenta2367913!
You've put a lot of time and energy into getting your monthly credit which should be automatic. At this point, an escalation needs to be filed which may wind up being a ticket so our system will begin to automatically credit your account. In this case, gramps28 is correct in whom you need to contact.
I am having the same billing issue regarding the "Friends and Family 2 lines on Us". In my case, the issue started right after I added two new lines with 2 for 1 during June this year on top of Friends and Family promo. Since then my bill does not have the credit for the two lines of Friends and Family lines. Before I added those 2 for 1, T-Mobile CSR confirmed that I can add those to my plan. Every month since, I have been on the phone with T-Mobile service manager who was trying to resolve this but I am not fully confident that my billing issue will be completely resolved. I have been with T-Mobile 14 years and always praise T-Mobile for being the market disrupter that provides the best value for the customer.