Too bad your salesperson is unavailable. Still you should find somebody responsible to complain, for sure he was not a private person but a business owner or employee. congstar is not your main contract partner, they don't need to resolve this conflict.
But a tip for the future: Do those things online. German law gives you the right to withdraw from a "remote deal" within 2 weeks after signing up, with no reason why. and probably you can review your T&C in English before signing. I understand this was impossible for this deal, but for future.
WRT smartwatch support: I agree, this is laughable what congstar offers. Worse than 3rd world countries? Hear Hear.
congstar, wake up! Even if it affects only the Apple Watch.
Happy new year to you soon, Crimson and good luck.