Incorrect exhaust adjustment leads to Check Engine Light issue

Supa Quick Fishers Hill (Bedford View), made incorrect adjustments on the exhaust of my vehicle by cutting off certain parts. Since then, the check engine light stays on. In the end, my mechanic confirmed that Supa Quick either damaged or removed the Co2 sensor and the initial problem, was not even a fault on the exhaust. After spending money on trying to fix this, I now expect Supa Quick to come forward and fix this issue once and for all.