WORST SERVICE, NOT TAKING THEIR JOBS SERIOUS

Took my car clio4 to bosch kemptonpark first time last year 2024 march, it had a heater problem and they diagnosed it to be having coolant problem, they claimed to have fixed it by changing the coolant with the new one and only to have the same problem in June, the same year... I took it back this time they spoke of a thermostat and they said they have replaced it, got my car last day of July and today 5 March 2025 experienced the same problem, when I call them, they don't answer my calls and wen I text them they don't respond, can anyone help me on how to take this matter forward cz I feel like I was paying for nothing