Mango airlines worst ever!!

Absolutely horrified with Mango Airlines!!! I travelled with my family back from OR Tambo airport. We were already checked in and arrived to the boarding gates 3 minutes after boarding closed as I had taken I’ll. The airline refused to seat us irrespective of us having our 1 year old with us. They did a check and the lady at the boarding gate mentioned that all the seats were full count, which I gathered that they may have give our seats to standby customers. They didn’t yet load bags onto the flight meaning that we could have still been seated! I am furious with the service. They wanted us to wait on standby for the next flight which was all sold out! Absolutely horrible!!!