that is why, always have a prepaid number which you can always give for taking these kind of connections. I always give my office number to these internet and any other type of services, so that whenever I move, the number is also gone. or else keep a separate prepaid sim for these stuffs. Just a few months back I have left the TIKONA(shifted from Noida to Hyd), then they sent some final bill on email id by delaying in disconnection(btw again this email id for for these stuff only, immediately created a rule to move anything from Tikona to SPAM folder), Cell no was my office no from Noida, so that is also gone. Now I will never here from again.
simple. If you get calls, block the number immediately, don't listen.
Interesting thing, when I left Hyderabad, I didn't pay last month bill(Beam telecom) and asked them to cut from security, said simply I won't pay, they can do whatever they want. Now when back to Hyderabad, Again took the same connection from them on the same old mobile no, still they never asked for old bill(though the incident was only 6 month old) and happily installed the extra box in the building to give me the connection.