Golf Cart Troubles, Please Help With Advice

I bought a Sunecarts 4+2 Solar lifted cart back in December. The next day we took it for a drive and encountered a serious issue where the cart was stuck on driving only 4mph and no faster. On Monday when the feed store (where we bought it) opened up, we confronted an employee who claimed to be an expert them and all he did was click some buttons and send us on our way. The issue grew worse and worse over the months. By March, we wrote the store some bad reviews and the owner finally took notice. He exchanged the cart for one that was supposed to function (of the same brand) but that had problems too within a week of getting it. All the owner has done since March is claim to be in contact with mechanics and even the manufacturer but nothing has changed. He just keeps stalling us and we don't even believe he's doing anything. This week, we pushed so hard for a return to the store owner but he refused no matter what claiming that the 10k he ripped from us for this faulty cart was immediately transferred to Sunecarts and he can't do anything about it but follow the warranty process which includes telling us a mechanic or fixed part is coming soon even though it never does. Please advise me on what to do cause I don't want to end up with a cart that can't drive a mile and a pocket that's deficient of $10,000