Tune up oil change

Hi, I recently had my car in for service. It went in for a surging problem in drive at a stop and an oil change. When I got it back I was told the cars cradle was rotten badly. However, the garage went ahead and did a tune up not asked for nor needed. When I asked why, I was told as a process of elimination for the surging. What I do not understand is do you not drain the oil before doing a tune up so therefor they would have known the cradle was rotted before doing it and notified me instead of costing me for more on a car I was being told was finished. Not worth putting more money into? If you could also give me an idea of what might be causing the surging. It is still doing it and I found out the information I was given about the cradle was false. It only had a very small hole in it. The mechanic wanted my Nissan for his kid. Unfortunately, I only found out after I purchased a new car. Now I am stuck with both. Any information you could provide would be helpful. I tried to upload an image of the cradle but not sure it worked. It appears my image is not allowed. What type of file do I need to use to upload a picture to you?
Thank you.