***** on Jet account

My husband has a Jet account which he has't used in years. due to his card that snapped in the middle and he has never went to replace the card. we received a letter from Jet last week saying he owes them R3500 -+ this was very weird due to the above. i mailed them to send me a statement to show me where the amount came from, and it was found that in July 2023 there was a purchase made at Sportscene for R3199.. i mailed them how many times to asked for a copy of the invoice to see who signed for the purchase. but i have had no feedback. i believe this is ***** that took place on his account,and i cant get JET to help me sort this out. we wont be paying this money, because we have never shopped at Sportscene, and if its *****, then we would like it sorted out asap