The latch handle connects to a cable, which in turn connects to the latch mechanism.
At the handle end of the cable, there is a crimped-on, L-shaped component that fits into a hole in the handle. The L is retained in the hole by a small plastic piece.
Symptoms you are describing can be caused by the small plastic retainer failing to hold the cable end in position. It will gradually walk its way out of the handle, until the handle ends up connected to nothing at all.
Alternately, it may be nothing more than an adjustment to the cable that is needed. The handle end of the cable has a typical double-nut adjustment (think of a bicycle control cable) to keep tension. If this is adjusted too slack, the cable will initially function at the limit of handle travel, but will eventually work itself loose and walk out of the handle as above.
Either way it's an easy fix. Buy the manual (less than $10 online), spend a few minutes removing the door panel, and the cable will be staring you in the face. Adjust as required, or if the retainer is broken/missing, substitute a zip tie. Permanent fix, and probably quicker than the drive to the dealer.
Now, if you are saying that the door fails to open from the inside or outside, then that's got to be a problem with the latch, and you can disregard the above.