I am not sure why they did not accept RBF transaction, but you should write to the support team and I do not think that your money will be in danger, even if you use RBF.
It's not that they don't accept RBF transactions, but rather that they don't accept zero confirmation RBF transactions. In fact, I'm fairly sure they don't accept zero confirmation transactions at all any more, despite what their website says, so RapTarX would have been out of luck regardless.
If you need instant orders in the future, then your options are either to deposit BTC to your Bitrefill account in advance and then pay for cards using your account balance, or to pay via Lightning.