no incoming or outgoing call?

bt dect cordless phone
There is a dial tone on the phone but when i ring there is no connection the message which is relayed back is the number is not recognised.All the numbers dialled are valid numbers ,similarly when there is an incoming call from another number there is a ringing sound but the call is not coming through on the handset. The bill is paid in full, there is a problem with the handset but i dont know what.