Adt Galaxy 16+ panel reset?

Hi, I have a ADT galaxy 16+ system installed in my home and cancelled my maintenance with ADT due to high costs. Now the panel shows that one sensor has been tampered with (is still flashing red and no tampering) and the panel shows code 80134 and asking for alarm company. They will charge £500 so want to know how to reset? I don't have the master code or engineer code so any help to get it working in the simplest way would be great. Thanks.