See if there is a price tag on the cart and the name of the supermarket on it. This is the only straw left.
Or you can watch the surveillance video and find evidence that you pushed the car out of the supermarket. This is a little too much.
Or did you use a supermarket membership card? Or a text message with a spending amount? Can be used as indirect evidence.
Do not ask for a refund, just exchange it. Some big supermarkets are more generous and may change. Might as well try.