Moikumbuec84
This is a public passenger-to-passenger forum, not the SBB customer service. If you want to contact them officially, use the (googable) complaints form.
As a fellow passenger, who can’t confirm your finding at all as regular commuter, I can only suggest the very obvious:
Find a different seat in a different coach, in case you found one with below average temps (significant differences do happen, also during summer)
Get suitably dressed for the current weather conditions and leave your coat/jacket on if necessary