We have some extraordinary talent on this forum and messages are read by those who genuinely care.
Thanks to this thread, I can confirm that Spark have confirmed I had been in 'lockout' due to fraudulent access identified by them as totally outside my historical pattern of use.
It appears they have robust systems in place far more than I ever thought.
Always using strong random passkeys, never duplicated across sites, changed regularly; it seems that some on the planet have the means to throw extraordinary resource at attacking target accounts and I really thought I was up with the play in protecting my stuff.
Seems this old dog needs to learn some more new tricks.