EASA Form1 - Block 10

I have a situation where a customer is having an issue booking serialised parts into their system.

The part is physically marked 1234-f, with the -f being a supplier internal control letter only, but the supplied EASA Form1 has only the serial number 1234 in Block 10. Subsequently the customer rejects the shipment due to the fact that the serial number on the part and the serial number on the EASA Form1 do not match.

Is the customer right in this situation and why? Any help much appreciated

would have said the customer is correct - your process should have a process in place for managing the control of parts.

If the part is marked as 1234-f then the F1 should be annotated as such.