Boonta, I had the same issue a week back after I had jacked up the car. After I lowered it back down it was bouncing all over the place and I couldn't understand what happened cause I didn't mess around with the wheel or tyre. My shock absorber was acting up but after a few days it settled again and it's driving like normal. Changing the tyre size on the wheels won't make it bounce unless they aren't balanced correctly.
If the guy fitted tyres which you did not select yourself and he fitted a size which is not recommended for your car and wheel then he needs to replace them immediately at no cost to you. Changing the tyre size without changing the wheel size will throw your speedo out (maybe not much, it depends on how big the difference is in the overall rolling diameter).
Like the others have said, get the tyres replaced and the wheels balanced first by someone reputable and then go from there and see if that corrects the car's behaviour.
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