disappointed and saddened

i took my car in for gearbox repairs, they told me i need a new gearbox after fetching my car, it showed the airbag light and hand break light, as well as the cabihole. they told me to take the car back, the mechanic of the car told me that i was lying regarding those things, he said they were initially there which is not true. now they are charging extra money to pay for their own mistakes. I am disabled and the car helps me alot when it comes to moving around because it is a need, i feel discriminated against. i have been calling them they are very rude and are no help at all. i am very disappointed and saddened by this whole experience and still don't have my car, its been a month now