Which Türk Telekom link did you look at ?
I am using this one to check my subscription status , invoices , usage statistics etc...
If your password works , then it must be this website you are looking for.
https://onlineislemler.turktelekom.com.trHow to extend my contract that will end end of January I don't however not know yet.
Since now I always went to the Turk Telekom main office and made a 2-year contract for phone and internet.
This time I probably have to find a way or use the call center to avoid the crowded office.
If you need a call center phone 444 1 444 is the one for Türk Telekom.