decline credit card - 3 different ones 3 times each

decline credit card - 3 different ones 3 times each
I can't pay for my 2seats =£7.10 as from England - only want to go from Sydney to Adelaide, in August 9th 2018.
Site keeps freezing, and can never speak to anyone / on computer. Can't even - at great expense phone them up to pay over phone.... Auto answer is useless. may have to cancel and rebook elsewhere

Domestic
Australia-Sydney
Australia-Adelaide