Price given for Reg change Incorrect and higher price given at deal time

these guys came to me and made me very very low offers for my 2 cars, I decided to accept , "already didnt feel great" however they told me they will sort out all the registration for R1200 per car, "he also showed me on his IPAD" next thing I know they here demanding R1500 per car which was not the original deal . they tell me sorry its thier mistake but I have to pay the fees regardless. i told him if its his mistake he must stick to the price agreed, I have his text saying R1200. needless to say I was forced to pay the fee, definitely wont be using them again