The door locks do not work

I had my van to a authorized dealer to have the door locks fixed, they would not open with the auto key and would not lock while driving. They fixed them and that lasted 2 weeks. This is the 2nd place to fix them only to have them last a short time. It is a real pain to have to reach across the front seat to open the passenger side as well as the back sliding doors. What needs to be done to have the fixed. I have spent over $100.00 so far only to have them stop working. I hate having to use the key to open the door. I was told they put in a new battery in the key and reset the computer inside the car. What is wrong that they cannot fix the problem? This is the only problem I have ever had with this van and I purchased it brand new in 2004. HELP