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Check relay. Sometimes there are two different relays for the high and low beam.
Another possible problem is corroded connectors at the headlights.
If everything checks out, there is a problem in the wiring. As far as dealership service, when you take your car in for diagnostics, they should check everything and if the new switch did not solve the problem, they should contunue diagnostics for free. It is a common problem, when dealer charges a set fee and suggest the easiest solution. Call them and tell them what is going on. When you pay for the service, the problem should be solved. And I know that those switches are not cheap.
Please let me know if you have any questions.