"No such file or directory" error mounting Azure fileshare

I am trying to mount an Azure Fileshare in Linux. I've gone through the instructions for setting this up, including installing cifs-utils and azure-cli, but am persistently getting a "No such file or directory" error:

root@laptop:~# sudo mount -t cifs //xxxxbackup.file.core.windows.net/backupfileshare /mnt/backupfileshare -o credentials=/etc/smbcredentials/xxxxbackup.cred,dir_mode=0777,file_mode=0777,serverino,nosharesock,actimeo=60,vers=3.1.1
mount error(2): No such file or directory

Most of the solutions I've found for this error relate to NAS appliances which don't support SMB versions 3+.

The issue appears to be network based, since I can connect to the storage account on port 443, but not on port 445:

root@laptop:~# telnet xxxxbackup.file.core.windows.net 443
Trying 20.157.157.242...
Connected to file-internetrouting.lon26prdstr05a.store.core.windows.net.
Escape character is '^]'.
^]
telnet> quit
Connection closed.
root@laptop:~# telnet xxxxbackup.file.core.windows.net 445
Trying 20.157.157.242...
telnet: Unable to connect to remote host: Connection timed out

I've checked with my ISP, and they say they only block ports between 136 and 139. In the Azure networking tab for the fileshare, I've tried setting Public Network Access as "Enabled from all networks", to no avail. Is there anything I might have missed setting up the fileshare, or anything anyone could suggest?

Linux distro is Ubuntu 18.04, with kernel version 5.4.0

Thank you,
Rob.