Overcharge at pump

I was on my way to drop off a CV, stopped at Total to fill up as I live in Johannesburg and am leaving at 5 tonight latest, I will not have time to fill up later. I know it should have cost me just over R150 as my car was just about half, and its a 35l tank. I decided to tell them to fill up, instead of saying R150 and a full tank could possibly cost me R180 or something, so rather fill up to capacity. Turned out is cost me R388.84 for 30.84l of petrol... I payed so they would let me leave. They said the manager was not there and I should come back next week. I phoned head office, they could not find the station to give me their number. I went online and found that garage, phoned the number on the website to get the managers cell number and got through to a car selling garage in Secunda... Really upset, have no idea how to sort this out.