Hello and welcome to just answer. Which switch was replaced?
Ok, then the problem is most likely in the TIPM (under hood electronic fuse box). When you turn on the headlights, a voltage signal is sent to the instrument cluster. Then the cluster sends a message over the communication network to the TIPM to tell it to turn on either the high or low beams. I have seen these TIPM's fail before, and my guess is that is your problem. The thing though is that the TIPM needs to be diagnosed using a StarScan scan tool or a newer style SnapOn scan tool. If your mechanic does not have access to one of these scan tools, then it would be wise to have the dealer properly diagnose this. Don't throw anymore parts at this until it is diagnosed. If it is the TIPM, then expect to pay around $500.00 parts and labor for this repair,
I hope this information helps, and let me know if you need more assistance with this.