Hello Mulfor4306,
Thank you for using Apple Support Communities!
I understand from your post that your iPhone is not staying connected to Wi-Fi which causes you to use cellular data unexpectedly. The following article has steps which will help resolve this type of issue:
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
Best Regards.
Thank you for using Apple Support Communities!
I understand from your post that your iPhone is not staying connected to Wi-Fi which causes you to use cellular data unexpectedly. The following article has steps which will help resolve this type of issue:
If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network - Apple Support
Best Regards.