Power Steering Pump problems of the 2015 Chevrolet Impala

Bought a pre-certified Impala, we were told that they had changed the power steering pump from the previous owner and everything was good. I just made my first payment on March 26, 2016 and that same day I went out and got in my car to leave from my daughters house and I pulled out about 100 ft and the steering wheel locked up on me, I could not turn the wheel at all. I turned my car off and called my husband, he came out and it done the same thing to him and then it finally started moving again so he took it to the dealership. They stated that it was ground wire to the power steering, so we said ok it should be fine. Today I went to stop at a stop light on a city street and the wheel pulled to the right and I turned it back to the left and the steering wheel would turn but it kept going to the right. Thank god I got stopped, it finally decided to straighten out and it was pulling to the right so now it is back in the shop and I am afraid to drive the car again. This has been a very stressful experience.