It sounds like your phone has a ring trip. I am sure the agent asked you to do this but just incase.
Make sure you have unplugged all phones from any ntl extentions you have and removed any "home installed" extentions, this should leave you with just one phone in your master socket. See if you get a dial tone or incoming calls with this. If not, try a different, working and preferable corded, phone into the master socket and see if this works.
IIRC ring trips are usually caused by either a dodgy phone, dodgy extention or having too much REN on the line.
HTH
Fingy