OK try this one, now I've hopefully read it correctly... :-) Check if your extension wiring has been reconnected so the wires previously going to 2 & 5 on your extension sockets now has one of them going to 3. Check each of the wire pair connected goes to the same socket connections on the slaves as in the master - and is a good connection with the punch- down done on a fresh part of the wire. What colour are the phone wires in the Master and the Slaves?
I've know a DTMF generator that couldn't cope with long numbers. It's power supply was fine at the start whilst a capacitor was charged, but when that charge was "used" it didn't like it. Could this be happening with the ring capacitor if your wiring is now incorrect?