I'm looking for some feedback on the following scenario:

We have a monitored security system fitted with a 3G coms module that has been experiencing coms failure. This failure is likely due to being in a Vodafone dead spot. Other than the occasional coms issue the alarm system has been working fine. Today a technician finally came to look at the issue and attempt a solution. During the course of this work the security system hardware has failed and the advice of the security company is that it needs to be replaced. The technician did acknowledge that prior to failure the system was working and that the coms issue had been addressed. It was only while conducting some subsequent coms test that the hardware failed. This particular technician has visited before for a routine system service and I was not inspired by his competence. 

What are the responsibilities of the security firm with regards to liability while working on equipment? I accept that equipment fails but I feel there's too much coincidence for the hardware to just decide that today was it's last day. Unfortunately this is also hard to prove. I am an electrician so I know full well that on occasion people do stupid things and break equipment but so far the security company doesn't want to accept that they might be at fault. The security company is a high profile reputable company, if there is any such thing as reputable in the security field, so they must have been in this situation before. We are most certainly not going to pay the technician $25 per 15 mins for the privilege of leaving us with a unserviceable alarm system.

Any thoughts on how to proceed from here?