Im in the UKIve set up shipping for the different prices that royal mail offer (Letter, Large Letter, Small Parcel, Medium Parcel)But when people order items from 2 different shipping profiles how do I get it to just do the higher price and not combi...

Recently when peopl are trying to checkout with multiple items in their basket is it making the postage shoot right up, I’ve not changed anything and never had this problem before I think it’s if they’ve added things from different postage rates but ...