I hope you don't mind me answering in English. ;) I think the problem is with your understanding of "get". This is a very flexible and common word, and not easy to explain in simple terms. "Get" can, as a concept, mean "receive" or "become". I say "as a concept" because sometimes you can use these synonyms literally, and sometimes you have to accept a general understanding of "get". In your examples, both "to be" and "to get" work with the same meaning. However, "get" suggests a change whereas "be" suggests a status. Compare "I was angry" with "I got angry". Both describe your feeling, but "get" suggests a change from one mood to another. If you're in doubt, use "to be" in passive voice. The more you use the language with native/advanced speakers, the clearer this difference gets.