^^ Not sure what else you can do.

T-mobile has a very 'German' customer service mentality - basically non-existent. AA seems to have happily given them the contract with their total 100% lack of inflight support, and couldnt care less about what happens after you buy a ticket. IMO

c-d: Maybe insist that they put you on the DFW-LHR flight that has working service on the day you leave? Ask about incoming aircraft and reported wifi issues on the plane that will be yours. Find out if your plane had reported issues and move to another if it does?

One thing I see with wifi, IFE and seats, issues are long running and take multiple trips to be fixed- planes run multiple 'legs' with the same issues. Heck, I recall an F seat that was broken for MONTHS.