Bad attitude from airport gate staff

I took a BA flight on 28 July'17 and firstly the flight was delayed. When the flight eventually boarded, the BA staff boarding passengers told myself and my fiance that there was an aircraft change and our seats had been changed. We then inquired further and she advised that not only had our seats been changed but we were no longer sitting next to each other. This is unacceptable as we had the same booking reference number, hence BA would have known that we were flying together. The above interaction was dealt with extremely poorly by a female staff member by the name of Khanyi. She was rude, unapologetic and extremely dismissive. At this point i was extremely dissatisfied with the situation and more so in the way it was being handled, and consequently approached the BA staff member Khanyi and advised that she is handling the matter poorly. She then clicked her tongue, said "i dont need to deal with this" and walked away. Is this is type of service we get for paying for a premium flight? Book with Safair, save money and get better service. I will not be flying with BA again.