Not keeping to offers made

Hello So i decided to sell my pick up. We buy cars came to inspect the bakkie and made me an offer after the sales rep left. It was just before christmas, i alredy had a other bakkie that i wanted to buy but that bakkie was only available after chistmas so 2 weeks go by and i call we buy cars, i spoke to the rep and asked him if we can negotiate a better price, he informed me that his manager said he is firm on the price so i sail its fine come and collect the bakkie. He called me the next day and said that they har reviewd the price and its now almost R50 000 less than the offer the day before! I lost my deposit that i paid for the other bakkie so that the guy would not sell it to someone else.