Mastercard complaint: Have been robbed of $50 by Mastercard

Purchased a $50 Prepaid Mastercard. Realized that the card only has 12 of the 16 digits printed on the front. Have tried resolving it several times, but each time I have been sent back and told that I need more information. They have told me they have found my card’s info on their computers, but there is always something else they need each time. I have been asked for an electronic journal from the store I purchased it from, a drivers license, a pay stub, a medical record, I’ve even been asked to mail it to them. It should not be this much work to get what I PAID FOR, I can give them any information they could want about the card, other than the last four digits, yet this is not enough for them. A big company like Mastercard does not need every single piece of VERY private information I have to launch an FBI investigation into me over $50.