Withholding deposit due to a missing number plate

Rented a vehicle from Europcar, after 2 days driving I noticed that the front number plate is missing and no signs of forced removal show. Reported the issue and was told to sign a claim form. 7 days later there is no response and I was told to wait up to 21 days for a response. I explained to the agent that is the number plate falls off it means someone did not put on properly and I should not be liable for it. I have spoken with 3 people already who promise to get back to me and NEVER do.

PLEASE REFUND ME MY DEPOSIT !!!!