iPhone 8 Plus said I was being hacked.

Such messages are scams. Your phone has not been hacked. Your phone does not have 15 virus.

Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

Unless you have jailbroken your iPhone there is no way that it could be hacked. Most likely you are a victim of a scam.

Ref: Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support