Refund request

I Took my Audi A3 In for gearbox malfunction, where the Invoice came as: Repair Mechatronic and Replaced Clutch. which was paid in full on (07-10-2022). the Gearbox was "repaired", with one year warranty. The car came back and i drove for at least 4783km (one Month), and it gave the same Gearbox malfunction error, i took the car back as a returned job, i was invoiced the replacement of clutch of which i paid in full (14-12-2022). Then i discovered that the clutch was replaced on the first invoice, i then requested for refund on (25-01-2023) for the second invoice, which they are refusing to grant me.