How does a debit order hold work?

[Maphobela88]

I rented a car at airport, 2 transactions debited from my cheque card separately and both reflected on my mobile app that they were deducted. Balanced also reduced. Within 7days, the merchandise sent me an email for the bank to release the hold but still 6months later the amount has not reflected on my card. Ask my banker ti follow it up and she said everything from their side is cleared. Who should then be contacted for further investigations