If you're not using the credit cards, can you not just simplify it? Say your credit card debt is £600 and you can afford to pay £100 a month.
Set up a category called credit card and set a target of funding it at £100 a month. On payday, allocate your £100 and pay it off (so in your account page it'll show a payment to credit card of £100).
Any extra bits you acquire through the month, add to that category. Say you have an unexpected refund of £50 - allocate that to the credit card pot. Then on the last day before, payday, pay that extra £50.
So your £600 debt is now £450 (£600-£100-£50). Interest goes on and takes balance to say £475.
You allocate the next months regular £100 and pay it off. Down to £375. Squirrel away another £50 over the month and pay off the day before payday as before.
£475 debt is now £325 (£475-£100-£50). Interest goes on and balance is say £350.
Rinse and repeat.
Very simplistic but a lot easier than faffing about. That's what I'd do.