I accidently made two accounts, and unfortunately this page was the top result for "deleting ultimaker account"...
I found the answer in a cloud security article, which says to email security@ultimaker.com about cancelling your account!
I assume the original asker figured this out, but maybe people like me who find this article first will appreciate it having the answer...
https://support.ultimaker.com/hc/en-us/articles/360012009799-Ultimaker-Cloud-security