Credits can't be exchanged for cash or refunded. They're for booking FC Urban games.
Plan credits are part of your 4-week membership, not a stored money value. They expire at the end of each cycle.
Pay-per-game credits never expire and stay on your account, also after your membership ends.
What you can do:
Change to a plan that fits how often you play
Buy pay-per-game credits only when you need them
Check your full credit history in My Games