Absa Fleet card service inconsistant

We have a transport company and we have Absa fleet cards. The fleet cards work very inconsistantly. I have drivers putting diesel in trucks during the early hours of the morning and sometimes their fleet cards work and sometimes not. When it doesn't work.. I have to make a payment in the early hours of the morning. That is if the petrol attendants has the banking details. It is extremely difficult to run a business like this. Especially taking into account that we don't even have a bank manager.