Horrible service

Had the most irritable and unwelcoming experience. Upon my arrival with my partner to our designated seats, we found that my seat was already occupied my another passenger which then means the seat was double booked. We then enquired with one of the flight attendant who was stationed at the back of the plane. She confirmed the mishap and advised us that there's empty seats and we can occupy them. We then proceeded to find seats and just as we were getting comfortable, another attendant then approached us and told us we can't sit on the seats we occupied and we asked her to direct us to where we can sit since we were inconvenienced by the airline. She was so unhelpful and her tone came of rude. She said anywhere while walking away without giving us any assistance. Having travelling with my pregnant wife, this made the experience sour as we had to walk up and down looking for empty seats. So unprofessional. Flight details are as follows FA846 seat 31F and 31E