Charges me thousands for no work done

Took my nivara computer box in to get checked. I told them there is a voltage problem. They phoned me and told me I am right about the suction valve voltage. They quoted me R5500 to repair. So they told me a lot of work needs to be done and will get the ecu next day. Wow in 1 hour they phoned me and told me it’s right. Like quite shocked I fetch it and plugged it in. Guess what same voltage as previously. Phoned a few times and then Ron phoned me at closing time. Told me they did excessive work on it. Which I don’t think they did. So please watch out for these clowns!!! They knock you like our beloved x president. I’ll will left no stone unturned!!! I’ll go up their asses with a magnifying glass. ****** *****s!!!