Wilson One Parking Dispute ('FIFTY' CREDIT)

Hi fellow Ozbargainers,

TLDR:
-I opened a Wilson One account with the voucher 'FIFTY' (January)
-Parked twice and $40 was debited on the account (April)
-The account was closed and a confirmation emailed to me (May)
-The $50 was reversed off the account
-Wilson One Parking charged me $30 on my credit card after the account was closed. (31/07)

Outraged! I am leaving this post for other noble Ozbargainers who need some guidance/discussion on what needs to be done in such an event.

I signed up a new Wilson One account (had never been a member previously) and was credited the 50 dollaroos. It sat untouched for a couple of months until I decided to travel interstate. Not knowing where to park, I turned to a Wilson parking lot, to which I was turned down and asked to drive to the nearest Wilson One car park (fair enough). Found the car park, parked there twice (2 separate occasions). The parking ended up costing me $40 which was happily taken out of the credit on the Wilson One account. A month later I decided to close the account. The lady was friendly and there were no issues in closing the account. End of June, I received an invoice telling me that I had to pay $30 and the $50 was reversed. I called the Wilson team up and they say that shouldn't have happened and they'd escalate/look into it. I receive another invoice and ignore it. End of July they automatically direct debited it off of my credit card. I am outraged that this has happened! So outraged that I had to sign in to Ozbargain and make this post!

I've been over the T&C's and I can't work out why they would reverse the credit and charge me $30 instead of $40.
I'm also confused why they didn't just direct debit me in the first place as well as submit the invoice. They had all my details anyway.
I've initiated a charge back with my credit card provider and they've agreed to credit me the amount whilst the dispute takes place.
As evidence I have screenshots of the T&C's from their website directly, the invoice and a written confirmation that the account has been closed. If anyone needs the T&C's screenshot let me know and I'll post it up.

Original Bargain:
https://www.ozbargain.com.au/node/355800
May be worth scrolling to page 2 where another member gets stitched up in a similar fashion and resolves.

Anyone else on Ozbargain that have been stitched up by Wilson One?