Cannot buy Windows 8

I heard of companies stealing money but companies not taking money is something different. For some reason windows upgrade assistant is not allowing me to buy the Windows 8 Upgrade; both PayPal, and the credit card. I have heard of the PayPal, and that has failed me twice. Now the credit card option has failed me even more times 4+! Has anyone experienced similar issues and ideally found a solution? PS I' am in Australia if this is of any assistance, and I'm trying to reinstall program and redo the process, to see if it helps. IE formatting!