Hi
If its not on the bank statement it hasn't been paid
So does your friend have other bank accounts that it may have been paid to?
Do they know that the invoice has been paid ?
If there isn't any record of payment I would reverse the payments and issue a statement to the client.
If payments have been made they will let you know and can provide details of payments. I love being the new bookkeeper as you can completely blame yourself for any issues while getting answers from suppliers and clients- The old I am working through the files and this appears to be unpaid..............
Hope yhis helps
Lisa