Mango worst service ever

Worst experience ever. I checked in online with one hand luggage. Fit my laptop, jewellery and perfumes in this one bag and when boarding the flight i was told I cant take my bag on the flight because I dont have a sticker on the bag . Why do we do online checkin if we have to stand in ques for bags?.now they forced to take my bag, yet cant even offer me free insurance in case my things go missing.worst service ever. Definitely find kulula and British airways and even safair attendants more pleasant that mango individuals. And in fact mango is not cheaper than kulula lately so from my side I will not book mango going forward. Disgusted