I'm soo hurt and disappointed

Nedbank Insurance appointed FOGI Plumbing solutions to come and fix a leaking geyser at my place. The plumber arrived, didn't even introduce himself, he went straight to the geyser and told me it's leaking from the valve so the excess fee is increased to R960, I told the guy I don't have the money since I was told by my insurance I'll pay R500 excess. He asked me to sign a form that says the plumbing was done satisfactorily which I refused. He left the geyser leaking like that. I'm not a plumber how am I supposed to know that the leaking is from the valve on the geyser?