I left a salaried role for the NHS back in the autumn. A couple of months later, I got a random letter from SBS, which appears to be payroll, saying they'd overpaid me. They gave no breakdown at all and no method of payment.
I spent some time trying to go to and fro with them and, mid-March, eventually got payment details. I repaid the money in full within hours.
Since then, I've got endless letters from them chasing the money. I've replied repeatedly by email saying I've paid it. They don't answer me - just send another letter. It appears to be with a collection agency. They're threatening to take me to court.
I can't get through to them on the phone.
I don't know what to do and the stress is driving me to tears.
Help?