Ignoring my pleas to refund the amount they overcharged me

This outfit recently moved me within Johannesburg and aside from arriving two hours early (at 6 am) and giving me a lot of stick when I told them they had to wait until the set hour, i.e. 8 am, the move went relatively well.

However, when the truck was unloaded and they were ready to go, I was forced to pay them an extra R300 in cash as the person 'in charge' refused to believe that I had already paid a deposit; he was unable to get hold of Rita, the lady who had arranged the move for me at the time.

Subsequently Rita has promised me over and over that they will refund this amount, however now they are completely ignoring my messages and emails about this matter and I'm not sure what else to do.