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going up hills it surges up and down speed by a few ks 50 km and under it feels as though it is thumping into gear

Without knowing more info, it's not possible to know what might be wrong, however with the little info you have supplied, I wouldn't be surprised if it's a transmission problem.If the vendor was a motor vehicle dealer, you may have some come-back under the Consumer Guarantees Act.

since i have had the car, i have taken it back for the radio, the computer on board, the brake plates to be skimmed, the pads were not changed we had to do that ourselves, the alternator had to replaced, the battery has had to be replaced, when taken to the mechanics about the transmission, the mechanic said there was nothing wrong and it was the way i was driving it can you please tell me what i should do next because i still feel there is something wrong with the transmission, i bought the car on july 10th and purchased a 3year warranty

If the trader is telling you there is nothing wrong and you are convinced there is, you may need to get an independant transmission shop to give you an opinion. However, make sure you advise the trader you are going down this path, as if it turns out that there is something wrong, you will be seeking to recover any costs for the assessment from the trader.
If there is a problem, you will need to present the findings to the trader and give him the opportunity to put it right. If he still refuses to help, you could have grounds to reject the vehicle.