You could give Motability a ring and say the constant bings and bongs are causing a distraction when driving and explain the dealer can’t book it in untill the 20th Feb. As @Carmad has said it’s highly unlikely Mb will let change the car withould the dealer looking at it first and are more than likely to put you in a hire car.
If the problem continues to persist after repair you are more likely to suceed in getting a new vehicle penalty free.