Pension credit is income-based. That is, they take into account any regular income you have, from whatever source, and that is deducted from your maximum entitlement figure (currently about £155 a week ?)

I think as long as you have kept them informed of any income you've had, you'll be fine. They are maybe just trying to sort out their own 'books'.

It is very rare that the Benefits people actually prosecute any minor 'mistakes'.... too expensive. I used to work for them.

You need to nip down to Citizens Advice mate. Don't panic.