If you happen to stumble on this, I faced the same issue as described above. Changing the partition to 64GB, 128GB would reflect in the VM itself, but the OS partition would still remain the default 32GB.
After looking at logs, I noticed some strange errors. Turns out my disk was way to full (99.9%). When the resize VM (ubuntu for example) occurs; Azure Resized the physical disk, then ubuntu performs the expand. Expand fails because there is not enough storage to run the process. This is why you're left with the same space.
- Delete some files on the VM (in my instance, clear /tmp)
- Turn the VM off
- Expand the Disk again (I dont think this is needed but I did it anyways)
- Turn the VM on. The disk should now show the correct size for /
If your VM won't even turn on, you can delete files using the recovery console documented here: https://learn.microsoft.com/en-us/troubleshoot/azure/virtual-machines/serial-console-grub-single-user-mode