As I said it should be supported. You said your watch works in two other countries with the same carrier. There is nothing wrong except when it is in Estonia correct? Then I would still say it is the carriers system at fault somehow. FYI none of us on the forums are Apple employees, we are users trying to help as we can.
worked in Cellular RF R&D for years and if my device works in one country with the same system but not in another country that says it has the same system I have no control over that. The is nothing in the hardware that keeps it working from in two different places except carrier control. You should Contact - Official Apple Support maybe they can sort it out. You can also contact your carrier in Estonia and talk to someone beside an operator. They have canned answers so you need someone on the technical side.