Nappies/diapers

What am I supposed to do when my baby doesn’t fit into any nappies/diapers?? I’ve tried the biggest sizes from 2 brands and one is a very bad fit and the other fits her ok for now but she will grow out of that quickly. She’s not even that big and two weeks ago she was about 10kg so I don’t understand why they’re not fitting when they’re for 15kg+ help