The overhead bins are for hand luggage, of which you are entitled to one piece. In addition you are entitled to a personal item, which could be a coat, to go under the seat in front unless you are in an exit or bulkhead row. Pragmatically, coats are unofficially allowed, but should be placed in bins if space only after luggage. In most cases this will be the case. The CC may hang in the wardrobe if fitted and space is available but this can’t be guaranteed either. CC appears to have been correct in their actions with you IMHO. It may be worth being a bag in your pocket that you can place your coat in to go under the seat if you don’t want to put it on the coat hook for your seat.