Well, I've some good news. Today I went to Digi Center and talked to the service consultant about activating Cellular on my AW. I didn't mention to him that I was trying to setup on AW4. He proceeded to trouble-shoot and after several failures, he asked me to remove the existing subscription because apparently, I had already subscribed. But I told him the setup was still stuck at activating.

So, first thing he did was to deactivate whatever setup that has been done. Next he proceeded to activate VOLTE which is strange because all the while I thought it was already enabled as this option was ticked in the Digi App. But anyhow, he enabled it for me on their end. Then the next thing was to unpair the phone, pair again and setup as new.

After that I was able to go to the Cellular setup page and where I clicked setup mobile data on the Watch App on the phone. Proceeded activating and following the steps and lo and behold after few minutes, unbelievably I successfully activated the Cellular plan on my AW4 

Just FYI, my model is A2007, not sure if it makes any difference compared to those who got it from the US. I checked this model is for Europe and Asia Pacific. So in summary, AW4 is supported for Cellular even though it was mentioned only AW3 and AW5 on Digi's site. Will go for a jog later without the phone and test the Cellular features. My only concern now is battery as my AW4 is the 40mm version 

Anyhow, I'm happy that I'm able to finally get Cellular enabled on my AW.