ADT honeywel security galaxy z-12 alarm system won't stop beeping every 20 seconds ever since the phone line got disconnected. It is driving my family crazy!

I've tried to call adt but I get told to send an engineer out to fix it. Yeah thanks at 130£

Can anyone help?

Many thanks if you can

The display unit is saying "alert! Enter code"

I do not have the key fob or the code as the system was here when I moved in

Is Phone line reconnected, being reused?
Are you renting?
If Landlord won't repair, give code or FOB, I would disconnect AC Power and Battery.