Hi @Domisa, sorry to hear about this. 
I have translated your question to English as this is an International forum, please post any replies in English.
Is this something that you have started to experience very recently, or have you not been able to send text messages for a while? Do you see any error messages when trying to send the text message?
Just to make sure that this is not caused by the network, could you ask a friend, colleague, or a family member if you can borrow their SIM card and insert it in the device and check if you are then able to send text messages. You can also try sending a text message to your own number with your current SIM card in the device.
Let me know how it went!
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