Yes, I agree, I would look for the phone number on the back and call, hopefully the code is still visible.
Take it to the store and they can probably tell you much is left on it.
They may want to know number on card. If it is not legible they may be able to scan it at time to pay your bill and that amount removed from your bill. If there is a balance after that. They should be able to tell you balance then.
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