Annoyingly, I am going through the exact same issue that you had earlier in the year. How did you finally get this sorted? I took out my subscription on Thursday, and still have the blank screen. TT have been pretty bad, tbh, but putting that down to weekend hours at the moment.
I got so fed up with the poor quality of the image and the service being so intermittent that I cancelled BT sport. Probably not what you wanted to hear!
Raise a new post on here, it was so much more productive than ringing TT, once one of the OCE’s had picked it up. I went round and round in circles on the phone and never got a solution to my problem.
Best of luck to you!