Problem with 2nd Handset for BT Studio 3100 cordless phones?

Cant seem to answer or make calls with the second handset of these phones. The main phone works fine and both bases and handsets ring out and can make calls but the 2nd on answer you cant hear anyone, and likely that they cant hear us. They were bought as a twin pack so no need to pair them, however i did try anyway, hope that didnt screw them up completely!