Veritas 8c Alarm blocked by installer?

I have a Veritas 8c Alarm fitted and have realised this year that it stops working every 1st May, which means I then call out the alarm company who charges me £54 to press a few buttons and away we go all ok, after reading messages etc I realise the installer has put a maintenance code disabling the alarm every year, therefore ensuring he gets his money. Can anybody help with info of how to sort this so that I never had to ring this guy again. Quite frankly I think this is extorting money out of a single mum with 3 kids, not a happy lady!