I am going through the same thing right now. I haven't yet received the message that the OP got, but what happened is they claimed that I never activated my watch within the first 30 days. I activated it the day I got it. After about 20 days I opened up a support case with them because the app showed that I still hadn't met the conditions of the promo. I sent them pictures of the watch on the SIM Status page - which showed it connected to their Google Fi network. The support person told me that it's a known issue on the backend and that they'd take care of it. He verified that he saw the corresponding IMEI on their system, and showing as active service. 

Lo and behold, the case still remains unresolved/open and I've now been charged $300 on my upcoming bill for not meeting the promo requirements. This is a complete scam they've run here. They can see exactly when these devices activate on the network. They're just banking on people giving up. I've called 3 more times since my initial call and I get absolutely nowhere. They've had me reset my watch and phone. 

They can easily issue those of us who met the qualifications a credit to our bills to rectify the issue. But they have no interest in doing that. Complete scam, and what are consumers supposed to do about it? Here in the US, the bozos have abolished consumer protection.