Migrated, changed Password, change lost after 2 days

[#1]

Migrated on Tuesday, changed to NEW password on Greenby portal on Weds. Accessed perfectly with new password via webmail and phone and pc clients, until yesterday Thurs pm. No access possible. Tried with OLD password and everything works. Oddly, i also paid for the service as requested. The payment is correctly recorded on the portal but the banner reads "only 29 days of service remaining, pay up" (my summary 🙂 ).
Has Greenby had to roll back account data for PHP or migration problems yesterday?
I used the password change function on the portal front page.
I still want to change my password, but not til i know it will be sustained.
I've raised the billing issue as a Greenby ticket but am very puzzled by the password issue. For example, what if I had used a generated unrememberable password for OLD? How would I have gained access to Greenby in that instance? Thanks
Can anyone shed light, please?

[#2]

Reads like a re-migration of the account, credential & all from a copy of the Plusnet platform.

I would not change any passwords until a month of trouble free Greenby operations has passed.

[#3]

@iscotter it was probably down to a 'fix' applied to some previously migrated accounts yesterday.