Problematic gearbox

I bought a car last week in midstream branch. The dekra report did not include that the car has a very problematic gears. The car has a serious problem with gears and I fear for my safety when driving it. I sent a complaint email to their customer care email address, no reply and any phone call to resolve the issue. I am so stressed out because I took the car to Midstream branch hoping to find a solution, only to be turned back and told I need to wait for a call from their call center regarding the solution. I can't wait any longer as the car is becoming very dangerous to use.