I took my subaru outback to Mrt to get it diagnose...

I took my subaru outback to Mrt to get it diagnosed as it had a stalling issue when the car was cold. I made mention to Quinton that I though it was the timing chain and he said it doesn't sound like it. Mrt kept my car for almost 3 weeks and were still having trouble diagnosing the car. My car was handed back to me with a dead battery, engine check light and a fuel symbol flashing on the dash, the mechanic said we weren't able to diagnosis it properly and I suggest you take it to subaru so they can diagnosis it and come back so we know what we have to fix. I went inside to get my key for the car and was slapped with with $415 bill, I asked what the cost was and I was told that the lower pump for the fuel was changed, the Labor and the diagnosis. I took the car in for a diagnosis and had a part taken out and replaced without my permission. While the mechanic was jump starting my car Quinton said "it wouldn't be a Friday if everything went right" once the car was running I called the mechanic to check the car because of the flashing lights on the dash, he took it into the workshop and came out moment later and said sorry we didn't connect the lower fuel pump properly, the fuel symbol was no longer flashing on the dash however the check engine light was still on, I asked the mechanic a second time to have a look at the car and he got his scanner and pressed a few buttons then the engine check light went off.
I refused to pay the amount they wanted as I was not informed of the part they change and I didn't get a proper diagnosis, they said we think its the timing chain. I will never go back to Mrt you claim to be experts with subaru diesel engines and I walked away with a bad taste in my mouth, and a car that still had the same issue, experts!! Don't think so.