If the wine is foul take it back, including the empty taster bottle. You will get a refund and then you can buy one that you like.
I would be as surprised as the supermarket if the wine was foul rather than not to your taste. The supers spend a lot of money tasting and selecting stuff to sell. They would want to know if it is as bad as you say.
I have no liking or connection with any supermarket by the way.
If however you had made the wine I agree with all the doctoring techniques mentioned before. Like the idea of dilute with a fruit juice then add vodka (or freeze).