Hello paulinagomezca,
Thanks for using the Apple Support Communities. It sounds as though you're having issues with your Wi-Fi connection dropping unexpectedly.
Does this only happen when using WhatsApp for calls?
What is the iOS version currently installed on your iPhone? Is it running iOS 13.6.1? If you need to update, you can use the actions provided in Update your iPhone, iPad, or iPod touch
Is your WhatsApp up to date? You can check this in App Store > Account > Updates. Update apps or use automatic downloads
If you go to Settings > Cellular > Wi-Fi Assist, is the slider in the ON position? If so, does disabling this feature help? If you'd like more information regarding this feature, please review article About Wi-Fi Assist
Best regards.