Discovery doesn't pay promised cashbacks

Discovery doesn't pay out their cashbacks as promised. We are still phoning and just getting new reference numbers each time about cash backs owed to us since Sep 2019, with minimal if any feedback... The card we used is my spouse's which was received in the post (in Aug 2019 - this after months of back and forth to just get an actual card since Mar 2019 when we joined vitality) and over the phone it was confirmed we should use that card until my physical card was delivered (which was only in sep) In aug 2 cashbacks were received using my spouse's card and then it stopped completely for the entire Sep onwards... Now they claim that my spouse's card was cancelled on the 31st of Jul already, yet we only received the card end of Aug and 2 cashbacks worked on this card after receiving it....