Q: Not receiving emails on iPhone 6

All of a sudden I'm not receiving emails to one email account on my iPhone 6 (iOS 9.3.3).

No settings were ever changed and it was working fine for years through several iPhone upgrades.

I can see all my email via webmail but they don't come to the phone.

I've deleted the account and added it back several times and the emails initially appear but no new ones come through.

I'Ve checked and re-checked POP settings (I have another email account with the same settings and it works fine).

I'Ve restarted the phone, switched from wifi to cellular and back etc but nothing works.  I'm using fetch and push is turned off.

any suggestions?