Inapropriate manner in treatment and unfair

Arrived at boarding gate (after checking in) 11 minutes prior to boarding. Told we were too late even though no where on the ticket it is indicated that the gates would close 10 minutes prior to departure. Manner in treating us was very disrespectful and rude when we showed them we still have one minute left. Had to pay R 6000 for another ticket at another airline. Boarding Gate E2 at O.R Thambo.