How do I stop my burglar alarm from going off even when dis-armed?

I have a Melcom ST6100 Burglar Alarm installed in 2004. We do not arm it at night while we are in, but on several occasions, it has gone of 3-4 times in succession, always at inconvenient times i.e. 3.00a.m. - 4.00 a.m. which wakes the neighbours up. One night the alarm sounded a total of 12 times and so I got mad and removed the fuse which didn't have any effect whatsoever. The firm who installed it, N.S.I.N. in Wallasey, Merseyside, seem to have disappeared from the face of the earth and their Telephone number is no longer recognised, so I can't ask them to come and repair it. Has anyone else had a similar problem with the Melcom Alarm, and if so, how did you rectify it? (if at all!) Also, I would be very grateful if anybody has the current Tel. number for N.S.I.N as well please.
Thanks in advance for any info.