Poor work from builder

I have a problem with a builder that is erecting two nu tech structures next to each other. He quoted me R108 000 with R23 000 going to an independent Electrician. He wantedR15 000 down payment and 2x progress payments. With the remaining money to be paid upon completion. He started work on these structures on the 23rd November 2020.and said he would be finished the 10th December 2020. Up to date after numerous progress payments leaving R20 000 for the final payment he has stopped working and these structures are 40 % complete. He was last here on the 17th March.2021. Structures are still only 40% complete in total. He doesn't answer his phone. He doesn't reply to WhatsApp or email. I would like these structures finished. I don't know what to do about this. I mean he has received 80% of the money and he has only completed 40% of work.