Unauthorised credit card transactions unresolved

Really struggling to sort out unauthorised transactions on my credit card. I have made several attempts to discuss the matter with the ***** department and the Credit card division, but the transactions continue. I have several SANRAL Toll road transactions on my credit card that are not mine. I can't dispute them or reverse them as they from a card that is not under my control. It seems that a card belonging to a relative has been linked to my account, so he is using the card and it's appearing on my account, and I'm liable for the amounts. It's been a while and I am really battling to sort out this account Card ending in 1087