Checkers - Sixty60 app not so fantastic when you need your money back!

I have had the most atrocious experience with Checkers and this app. So the app pre-authorises an amount higher than your basket to account for different weights and stuff if you buy meat and other weighed items. So you need to have basically double the amount of your basket for the transaction to go through. Then Checkers fetches the actual amount from your bank and leaves the pre authorised amount just lying there uncleared. So what the bank doesn't tell you is that this amount will never be reversed to you unless you call Checkers for a clearance letter (which I have been doing unsuccessfully since 7 August because all they can do is 'escalate' the request) to then send to your bank to release the money. They dont tell you this and you then need to resort to social media platforms to get any help at all from them! The call centre staff are patient and I understand they can only do so much, but Checkers is really ripping people off here, making them sit with no money for almost 2 weeks. This is so unfair and appalling, Checkers really needs to fix their app and this issue. PS - Can someone please help me get this letter ASAP as its now been unreasonably long for me to keep asking and waiting.