Bad service by Bertis (ETG Africa)

MY solar geyser was installed 2020 by Bertis,then 2022 he contacted me that it's due for service,I paid the R850 he requested till today nothing happened and paid last year August ,he kept on promising that he will come he hasn't come he keeps telling me his in polokwane and and,some day he will make you stay at home and say his coming now my solar geyser had low pressure you cannot access water in your bathroom and kitchen same time and I didn't want someone to come and touch someone's work because if there is a fault they will blame the next person,tried to request refund and he said he cannot refund me so tired of calling him ,texting him and calling the office