Questionable business practices - not recommended

Questionable business practices - not recommended

Have ordered items, then a bill including shipping costs received. The bill was paid and a week later came the package, so far so good. But there was also another bill with renewed shipping costs
On my request I was told that it is unplanned to several packages so the cost -> but it was only one (almost 7kg) -> Next answer was then: "We get the freight charged by our manufacturer and give this to you. " Shipping costs in total 44

As a "mail order" you should already be able to state his costs and not in retrospect, his customers off the head - I would like to know beforehand what all costs me in total ...