How to achieve the right shipping costs with weight?

Hi, I made Shipping rules and added weight to every product. It works here and there, but when it If it comes above a certain weight it doesn’t work.
For instance, I add dadi oil with a weight of 17.5 grams which is assigned to Brievenbus 1: 0-100 grams = 2.50 €
When I add Peclavus Voetcrème vettend, it becomes Brievenbus 2: 100-350 g 3,50€
So far, so good. But when I add more items then it suddenly has just the option of pick it up (afhalen). It should however show option Brievenbus 3, which is 350 -2000 grams 4,25 € or Package (Pakket) which is 2 – 5kg. 6,99 €
There is also Pakket 2 with 5 kg – 10 kg 9.99€
What now?

Also I do not understand the difference between these Shipping rules and the ones you add under shipping zone. If I work with both I get more options to choose. I just want one method that works with adding up.

Thanks.

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