Originally those 2 wires of the alarms auto dialer would have connected to a BT socket terminals 2 & 5. Terminals 2 & 5 correspond to the BT cable that comes into the house connected to line A & B at the rear of the socket. If you had a older system, you will find terminal 3 was also connected when you pull the the front of the socket off. Terminal 3 is the bell wire for the telephone.
PS ^^
You should tell the alarm company you sorted it for a fiver 😂