The 85% was incorrect - but only impacts this financial year - doing my calculations again with last year not this year thresholds looks like the amount I owe is correct - boo - but hooray because I am due some money back from childcare for the past 6 weeks where somehow they were using the 85% of CCB rate.

Man the system is confusing, if last year hadn't worked out as a debt - not sure if I would have found the problems with this year!