15.4.1 repair
Since I updated to 15.4.1 only my Wi-Fi service works, my cellular service doesn’t work for phone calls, messenger or WhatsApp although FB app and the web browser work. How to repair?
Try first to optimize the range of the mobile network, see this Apple article:
If you see No Service or Searching on your iPhone or iPad
If you see No Service or Searching on your iPhone or iPad - Apple Support
Check the Wi-Fii connection, see the following Apple articles:
Connect to Wi-Fi on your iPhone, iPad, or iPod touch
Connect to Wi-Fi on your iPhone, iPad, or iPod touch - Apple Support
See this Apple article: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network
If your iPhone, iPad, or iPod touch won't connect to a Wi-Fi network - Apple Support
Recommended settings for Wi-Fi routers and access points
Recommended settings for Wi-Fi routers and access points - Apple Support
If you need help with your Wi‑Fi password
If you need help with your Wi‑Fi password - Apple Support