Engine warning light caused by your technician

I’m having an issue with this company. I bought a car in February it was in good condition. I then installed car track 2 weeks later my vehicle started to display engine warning light I called the company they came to switch the light off with a diagnostic without checking the actual problem they caused. 3 days later the light came back again. I called they came to remove the device but they did not switch off the light. I took my car to mechanic, I found out that they have tempered with the wiring hence there’s engine warning light. I called the company to come and fix the issue they never came. They kept on debiting my account while there’s no service. I decided to reverse the debits so they can call me. They did call but never actioned my issue now they want to handover my account to the attorneys. How fair is this. I don’t have the device in my car yet they want me to pay. This company they are a bunch of ****mers I won’t pay for something I don’t use. They must just get back to me ***