How to stop constant "Alerts" on an ADT alarm system?

Previous owner had ADT System, which I never had activated when moving in 6 years ago. Internal "Alerts" require entering a code to clear. These alerts were very infrequent - 3 or 4 in 6 years. However recently they became daily and now almost hourly. I am in my Eighties so would appreciate some advice as ADT were unhelpful saying if i wanted their help it would cost £250 per visit.