Hi @moresmarian, sorry to hear about this.
Your post has been translated to English as this is an International forum, please post any replies in English and it will be easier for me and other users to assist you.
Have you been able to try changing the network type to see if the calls work better on for example, 3G or GSM? To do this, Find and tap Settings > Network & Internet > Mobile network > Preferred network type.
Another thing that you can try is to insert your SIM card in another phone or tablet to see if you can make or receive a call without it being dropped. If you can make or receive a call with another phone or tablet, it may indicate that there is something wrong with the software of your Xperia device. Try to fix this by performing a software repair using Xperia Companion. Keep in mind though that a software repair will erase all user data from the phone, so it is advised to do a backup before the repair in order to prevent data loss.
If none of these measures manages to improve the quality of the phone calls, I would suggest that you get in contact with your network operator as this might be related to the SIM card or the mobile network.
Let me know if that helped!
