So they have been doing works in the SE3 area of London and people have been unable to use their phones for over a week. Yet they don;t even bother putting up info about it on their site and the customer service staff don't even know what the works are or how long it will last

Who says that maintainence is going on? SE3 is Blackheath, always been dodgy for TMobile coverage. I know there's been a drop in in the signal because of the tens of thousands of Olympics crowds in Greenwich Park (served by the same tower).

use orange?

Can't use orange either.

Some stupid customer service bloke claimed they are doing work in the area

Why was he stupid? Why don't you believe him?