Gearbox Problems

I took my Fiesta to Gearmax Bloemfontein to change only the selector seal. My gearbos was working 100% with no issues. When I got my car back the car did not want to go into 3rd gear and it kept on jumping out of 1st, 2nd and reverse. I took it back to Gearmax where I was told it is the Links. I said ok and I went and bought new links from Ford and paid Gearmax once again to replace the links. My car still did exactly the same and I took it back 2 times where they said all is fine and they did nothing wrong, but I never had issues with my gearbox until Gearmax worked on it. I am not sure if they damaged the selector shaft, but I am very unhappy about the service as I was told Gearmax is the best, but the service I received was bad and I don't have the funds to take my car to Ford to sort out the problem.