Yes, as long as you haven't spent them. We refund unused credits you bought within 6 months of the purchase, back to the payment method you used.
How to ask
Open a support ticket and tell us which purchase you'd like refunded. There's no refund fee.
What you get back
The unused part of that purchase, in proportion to what you paid. So if you bought 100 credits and still have 40 of them, you get 40% of what you paid back.
What can't be refunded
Credits that came back to your balance
When a curator misses the rules, or you cancel an ad, a package or a Hot or Not request, the credits return to your SubmitHub balance, not to your card. From there they're unused credits like any other: spend them on something else, or ask for a refund as above. See the "How do I get a refund for a submission?" article for how those returns work.
Do I have to decide within 6 months?
Only if you want the money back. Credits themselves don't expire, so you can keep them and use them whenever you like.