Activity not uploading till I'm on Wifi even though I have a working SIM card

I just got a replacement K2 for the elevation issues (which seem to be fixed so far - I have completed 2 rides), however my activities are now not uploading after I have ended the activity.  The SIM card is the same one I had in my previous K2 and it was working perfectly then.

I still have data on my SIM and its not de-activated or anything like that.

I have already done the basic troubleshooting - removed and re-inserted the SIM card, but the device is still not uploading my activities till I get home and the K2 connects to my home Wifi. 

I know that I can connect the K2 to my phones Wifi by enabling the hotspot on my  phone, but I want to get it working on the SIM itself as I need to use the tracking enabled by having a SIM on the device.

TIA