I have the same issue. I set maximum storage last year for my tenant to 5TB. I used to work because one on my user could store more that 3TB in his OneDrive.
But it seams that things have changed recently because all user are back to 1TB storage limit again.
I have just bought a OneDrive plan 2 and assigned it to my user with more that 3TB of storage in his OneDrive but nothing changes.
I'm in contact with Microsoft support but they don't answer to me (asking for screenshots, ...etc.) and gives no hand...
Looks like a bug or a change in their policy.