The watch should update regardless of the phone being used. However, as you say, a Samsung phone is needed for the ECG and BP functionality to work.
In both the cases here, the members are stuck on 126.96.36.199.
The only other issue might be the make of your phone. Is it a Samsung?
You will probably have seen from other comments in this thread, that the latest features only work with Samsung phones.
I have the same issue "service not available in your country" watch is 188.8.131.52 Galaxy 3 purchased from EE and the the phone is N20U5G N986BXXU2DUF8 with the latest updates and with EE.
Any help appreciated.