Dishonest repair company

On 2/7/20 my husband sent our microwave for fixing to a company called 1AA Appliance repairs that is based in Phoenix Durban, it is a mobile repairs company. It is owned by a guy named either Shaun or Mervin (he is being dishonest about his name). His cellphone number is ***. He assessed our microwave & said that the Magnetron in our microwave is damaged & it costs R350 for a new one, with labor the total cost is R480. We sent our microwave in for fixing, it was returned the day after & it only worked for half the day. When my husband opened the microwave cover, we saw that the magnetron was not changed, it still had the same old magnetron that rusted & dusty (we know this because my husband had opened up the microwave prior to us sending it for fixing & he had changed the fuse & also tried to check if it was the Magnetron that was faulty). In actual fact it was the microwave door that was faulty that prevented the microwave from working. We contacted the owner numerous times to rectify this problem & he refuses to give us a refund for the Magnetron. Please can I have assistance with this matter.