For those of us that have an easyMobile SIM and want to remove the automatic overdraft applied to every SIM purchased from them....
Go to https://www.easymobile.com/selfcare/emcontent/cust_services/switch.html
Use their live chat client and let them know you wish to cancel the automatic overdraft facility.
You'll need your website login information and your phone number account you want to remove it from.
They'll do it there and then, so they won't be able to take more than your credit balance allows. It's also free to do this, no charge at all, but ask them if that's so when on there.
You can also ask how to stop automatic top ups from your card if you have that option activated. But you can't have that removed in live chat.