Bags taken when boarding with valuables

I just boarded flight MN603 and had a single hand luggage bag. Staff tried to take away my hand luggage as it was a trolley bag notwithstanding letting many other passengers with similar sized trolley bags take their bags on the plane. My bag had medication for the flight as well as many valuables as these should not be placed in check in luggage as insurance generally doesn’t cover the loss of these items, expecting them to be in hand luggage. Whilst I understand that full flights mean less space, I paid for a flight which entitles me to a hand luggage. It was the correct size and weight and I had no other bags or a lock with me. Passengers with more than one bag should be asked to leave bag. In any event, there was additional space overhead (as many passengers had no hand luggage at all) and below the seats and passengers boarding last should be asked to leave bags once the cabin space is full. Further, if something is ******, would Kulula cover the cost??