Line reconnected this morning at 66/19, up from 38/9. which is fine. Speed tests are showing upload has increased from 9 to 19, which is also fine, but downstream is still running at around 35Mbps, which is what it was before. Looks like It's still being throttled at the servers at the old setting.
I remember, some years ago when I upgraded from ADSL to Fibre, speed didn't increase until someone intervened to "throw a switch" on the server to unthrottle it. Might this have been overlooked again?