Gas cylinders issue

The Gas Man did a gas installation for a gas stove and a gas heater around June 2021 at my house and then he came to install 2 x 14 kg gas cylinders just before I moved in around 01 September 2021. My house plan states 2 x 19 kg gas cylinders must be installed and I also paid him for 2 x 19 kg gas cylinders. He installed 2 x 14 kg gas cylinders because he said that the gas cylinder supplier had a shortage of gas cylinders at the time when I moved into my house. He promised to come and exchange the 14 kg gas cylinders to 19 kg gas cylinders as soon as the supplier has stock. I have been trying to resolve this matter with him since October 2021. He is avoiding my calls and he is not answering my whatsapps. His companies google reviews is full of negative comments about him avoiding calls from customers. I need him to replace the 14 kg gas cylinders with 19 kg gas cylinders.