What to do if someone doesn't give me a refund?

They promised me an iPhone. I found out from and Instagram I'd. So the total amount to be paid was 4k but when I paid 500 in advance he asked for more 3000, when I paid that he asked for 6600 more and I paid that then he said he can't refund because of account limit is 20k so asked for more . And when I refused to pay more, now he refused to refund and now isn't replying to my texts or calls.