Overpayment of a CIS Contractor (supplier), they refunded

Hi i have overpaid a CIS Contractor in error. They are CIS Gross.  They and two invoices on my system £2000, I paid them £2780 in error.  They have repaid me through back transfer the £780.00.  I didn't know now to record it. They credited their account with the £2780 bro clear the invoices but there is a credit on the account of £780.00.  i can't match the refund to the account