GUMTREE REJECTS MY BANK CARD

Gumtree is excellent in posting free ads, but you cannot reach anyone there personally. All you get is a webpage and Q & A with most common problems. My problem is that I WANT TO PAY THEM for boosting my advert, but after getting a new FNB card, their system throws out the payment with öoops - this is embarrassing - try again. The "problem" is apparently my anti-virus. Now how on earth do I fix that? Surely a lot of people change bank card details. I filled in a message on their webpage: no reply. I even wrote a post on their FB: no reply. Sooooo. Can't pay them, can't boost my advert. Maybe Hello Peter has some secret information how to get a one-on-one? PLEASE someone out there, help!