If this is a recent development then chances are RogerL is on the money.
You can use a multimeter or a simple circuit tester (one of those “screwdrivers” with an alligator clip attached with a short wire) to confirm the wiring on the plug on the car. Google your connector to get a wiring diagram, clip the alligator on earth and use the probe to test the relevant connector. Just remember to turn on the indicators on the car! You should get a rhythmic blinking/reading.
You can also get special testing tools for connectors, but for one-off use that might be overkill.
If someone has mistakenly switched left and right it’s an easy fix (open the covering for the plug and switch wires). If that’s the case then I would have the whole connection looked at by a professional just to be certain that was the only mistake.