cannot reconcile account

I booked a rental car thru them end of July 2015. They deducted a holding amount and promised us that within 7 days of returning the car, they will reconcile the account and return me the difference. As yet, after asking numerous times, they cannot reconcile the account, neither produce a detailed account!! They said they would escalate for investigation, but that also seems to be going nowhere. It is now 44 days since we returned the car !!!