I didn't get ARX from VO mining either, got plenty from exploring, a little from combat and some from 'other', which seemed to go up when I spent money on a python and upgrades yesterday
I get the feeling that VO mining or perhaps mining in general is so Credit heavy that it would blow out your ARX limit too quickly.
OP - Not dared to buy ARX yet, until things have calmed down with the bugs etc, so again, sorry for the hijack. I doubt you'll have trouble getting them eventually. If the transaction is logged on your PS account and still no ARX in a week, then it's refund time from PS until fixes get fixin'.