Slow in deposit refund

When I returned a rental vehicle after one month's use, they did the routine checks on the car, and I was refunded the deposit within a week. Then I leased a vehicle for 7 months. I have just returned it, and the same checks were done as for the rental car, but now they say it may take a month to refund the deposit. The car was serviced less than a week before I returned it, and no issues found during the service. Who knows what they may be doing with the car in this period, and hold me accountable for....