Water cap not closed

I went to the petrol station on the 22 December 2019 to fill petrol and to check oil water and tires the petrol attendant did close my water cap. I realised that when the car started coming out smoke maybe +-20km from the garage. I went to the garage to report the matter on the 03 of January as I was not around and the guy by the name of Andrew advise I go fix the car and bring the invoice then he will reimburse me. I took my car for a repair submitted the invoice then Andrew only pay for the labour which was R600.00 and he request for the invoice of thermostat that got damaged and replaced, and he wont pay me until I submit the R1400.00 invoice for the spare part