What is up with my gas powered remote control car (HYPER 7)?

I have recently purchased a gas powered remote control car, its called a Hyper 7, the problem is even when i have put new batteries in the transmitter or the car itself the accelerator isnt responding fully to the transmitter, it sometimes does respond but mostly it does it by itself or not at all, i have spoke with the person whom i got it from and they said it must be the batteries but i have tried that and it dosent work, he isnt avalible to ask another question hence the reason im asking on here

Get a refund with out questions..
Merry Christmas..