It really depends on what they consider "the system". Are they really just saying the load center, maybe just the breakers or they might mean a total rewire. That is a question you really need to understand.
I would want some clarification but my guess is they are just looking for a way to cancel you. Insurance has gotten crazy in the last few years and companies are doing irrational things.
As for your situation, if you have the slots I don't see a problem using that panel. The real question is whether you have done a load calculation. That would be the first thing I would do. Car chargers are continuous loads and you need to be sure you have the extra capacity..
