I tried one of the Kogan $1.00 deals for 3 months paid via paypal all went well received sim and got it up and running.
Through my own mistake it automatically topped up from my credit card with an extra large 90 day prepay $188.70.
No way am I ever going to use that much prepay plan being 78 years old,  i'm quite happy with my skinny $9.00 plan.
I have been in touch with Kogan = On the main page of dashboard you can find 'Recharge' option. Selecting that option will give you many plan details from which you can purchase any plan as per your wish.
Once you downgrade your plan, you can get back to us with card details for verification so we can raise refund request of 188.70 for you.
I have looked on their website to try and change to lower plan but can't seem find a lower plan.  And was afraid if I click on another plan therefore incur more charges!
I have a couple of options to port my existing Skinny number to Kogan not sure how you can do that?  Or sell the $188.70 sim card to another for about 150ish.
And forget about Kogan altogether.