Well what a suprise, you offered as solution that would cost them a lot of time, effort, & money to challenge, and they backed down, albeit for now!
Just two days ago I had an email from Mamut asking me to contact them with regard to migration to their software.
I say you need to keep going as I don't trust them.
One question, if we have already used the test confirmation codes you issued, will MYOB's confirmation codes still work?
Thank you for your hard work which I'm sure has not been in vain.