Vandalised by Window Repairman?

My tenant reported via the estate agent a leaking window. It turns out the damage is quite extensive with some internal drain having not been set properly inside the wall (something like that). Anyway…

I requested 3 window repair contractors to quote on the repairs and one of them went ahead with doing the work of replacing the silicon seal around the window and asked me to pay £75.

I forwarded him the email I had sent originally which clearly shows I only asked for a quote to be done and I said that it’s illegal to carry out and bill for repairs that were not authorised.

He threatened to remove the silicone and may have already done so which means the window would be in worse shape than before! Does that count as some kind of vandalism and should I report it to the police? Report it on his yellow pages advert? I don’t think I should support dishonest contractors who do work without authorization and bill people. The point of getting quotes is to not get turned over?

Thanks for advice
Grant