no refund for false advertising

Saw an ad for a vehicle for sale on junkmail. Put in an offer for the amount advertised. Got an invoice from gumtree stating what needs to be done for the sale to go through. Did everything they asked. Then the client came with a different amount after the amount had been paid told him to cancel the transaction and he said it cannot be done as the goods needs to be delivered and rejected on delivery before a refund can be done. Now Gumtree says that I need to pay the balance before I can receive a refund or it will take 7yrs. The amount on the invoice was from them and was the advertised amount which was paid. I want a refund as the client wants a higher price for the vehicle that was not accepted by me.