Poor service

I was travelling from Polokwane to Cape Town. I took the SA link flight from Polokoane at 11:55 to OR Tambo. I then took a Brittish airways flight (6425) at 15:00. In Polokwane I got 2 tickets so that I don't have to check in again. The guy who served me said he will arrange for my banner to be collected in CPT. So that I don't have to collect it in Joburg and check it in again. When I got to Cape Town, there was no banner. I went to ask Amanda in the baggage office. I did not like her response when she said they cannot find it and if they find it they will call me to collect it. I then requested to speak to someone that I need to complain to. I was referred to Liezel, she said she can't help unfortunately. ''Their policy is just like that''. How do I explain that I lost the bunner at work. I have a proof that confirms that I left the banner on the safe hands of the air travel. Can someone help. I've asked Liezel for her surname and she said they don't give out surnames. She is the only Liezel at Brittish airways and there is only one AManda at brittish airways. WHAT DO I DO. I AM FRUSTRATED. I left the banner with them because I trusted them.