Depending on the local laws, the 2x return of your deposit may not have been a mistake. They may have been legally obligated to return 2x of the deposit amount

Depending on the local laws, the 2x return of your deposit may not have been a mistake. They may have been legally obligated to return 2x of the deposit amount because they failed to return your correct deposit amount within a certain number of days. Example: 21 days for some areas