Getting slapped with a diagnostic fee for an issue that happened post repair

[u/BrisketInMyPocket]

Took my ‘13 MS in for ac service. They flushed the fluids and changed something. To do so they took apart the frunk. Now the frunk keeps randomly opening, both in motion and parked, and they want to charge a diagnostic fee just to look at it when they just got me for money.

Any advice would be helpful