1998 Mazda 626 transmission repair

Transmission problem
1998 Mazda 626 6 cyl Wheel Drive Type unknown Automatic 152000 miles

My transmissiion went out in October I ask the repair place to give me a total transmission rebuild, the first time they put it together it didn't work so that had to put it back together. I got it out of the shop on 10-16-2007 and paid 1850.00 for it on 11-30-07 the car started to sliping and would not go into reverse. I took it to the shop and could not get up the hill and found my self on a main street in lots of traffic and scared to death, today they tell me that they have been working on the car and the best they can come up with is the oil pump went out and caused the transmission not to work. I don't know cars and I am a granny taking care of 4 babies ages newborn to 6, Is what they say possible or is the car company trying to take advantage of me? Wanda