Deduction of money not what they promised

We recently moved from Parklands to Burgundy estate. I phoned customer care to move my gym contract from Parklands to Plattekloof. They promised that it will be moved and ready by 1 October 2015 and will be paying R399 per month. When I got to the gym my contract hasn't been moved. I phoned customer care again to move it and the told me I must pay R499. I gave them the reference code where the said R399 to move. They send me a mail telling me they made a mistake by telling me the wrong price, but now they cannot give it to me for that price so I have to pay R499. This is unacceptable. I feel if a price was promised to you and it is on record they must give it to you at that price.