Xperia xz no text notification sound

[Kaywebb]

My partner has the Xperia xz premium and I have an iPhone 7. The last few days when I send him a text message he doesn’t receive a notification sound.. this happened when I had the iPhone 6 but an update was available and it seemed to sort itself out, anyway last few days this is happening again, I’ve reset my iPhone I case it was that, but he’s not keen on resetting his phone just in case it a nothing problem that can be fixed. Any ideas please thanks 

[Uliwooly]

@Kaywebb

Does he gets the message but no notification ?

or

He doesn't get the message at all?

which app on your iphone are you using to send the message?

[Kaywebb]

He gets the message but no sound. He gets messages off other people who have iPhones just my phone seems to be a problem. I’m just using the usual iPhone message? 

[Uliwooly]

@Kaywebb

Which messaging app is he using?

[Kaywebb]

just the Sony Experia text messaging, he hasn’t downloaded any just using the one that’s on the phone... 

I did email Sony support and they couldn’t tell me what was wrong?! 

[Uliwooly]

@Kaywebb

Does he has a different ringtone for you? if you call him, does your call goes straight to voicemail?