Tuffy Tire and Auto Service Careless mistake service that causes safety issue Plainfield, Illinois

I took my car to Tuffy on Feb 2014 to fix for engine light on service to pass the emission test. They replaced the EGR and did other engine work which cost $1154. I past the emission test after 2 times. Later on Sep last year as my wife was driving the minivan next to PEHS high school the car stayed at same speed round 45-50 mph without slowing down. The only way to modulate the speed was to press the break to come home back safely. I towed the vehicle to another shop and they found the EGR gasket inside the EGR casting housing. I addressed the issue to Tuffy for service refund and they (store managers César and Owen) denied my request several times when contacting the owner 'Sam'. The cost of EGR valve with labor is about $400. Their policy is 'If it is not done right 1st time it is free' but they are working against their policy.