Extremely unprofessional and poor workmanship.

I gave in my Land-rover gearbox to be overhauled at the company. Paid the R 8 550.00 in full. When putting it back in, I realized that there were parts missing, and that it was in worse shape than before it went in, squirting oil out. Before taking it to the company everything worked, just not as well as it should. When phoning them - I was upset - the lady at reception became extremely defensive and rude. While insulting me over the phone, not one word was mentioned about my gearbox. Photos were taken, so me and my daughter took the photo's to the company. Upon arrival, the lady just went on where she left of over the phone. She was extremely unprofessional - swearing at us, and shouting hysterically. After a while a gentlemen arrived, and we could eventually speak to him like grown ups. During the whole episode in their office, she - again - did not speak one word about the gearbox that was paid for in full, did not work, and was incomplete. The gentlemen admitted his mistake, and gave me one of the missing parts. I lost my money, and my gearbox doesn't work. There is a 6 month guarantee, but I can't trust them. It is going to cost me a lot more to fix it - again. Please help.