swich phone number to at&t from t_mobile?

[mmmmSHENZHEN]

I have a family plan under t_mobile serive ,it due at 18th october ,when I can swich phone nuber to at&t ,at&t said that once I order the phone they will swich the phone number right away, t-mobile said if I swich phone number then they had to cancel my account right away and charge some termination fee if I do this before 19th october .
I just dont know what to do, if I order new phone and swich phone number at 19th , that takes 4 or 5 days to get it since i order it online ,that means I would not have any cell phone to use during that time, and even this is ok to me ,there is still another proble ,if i do this at 19th , my contact is due at 18th already ,t-mobile still let me transfor my phone number to at&t? is my phone number still avaliable at 19th? i heard that if my contract is due then I will lose my phone number forever.
need your help thanks
I am in colorado