I have been told someone with access to my iPhone has hacked into my Amazon account — how can secure my iPhone

And in a few minutes after than my credit card is compromised.... I am working with my bank trying to recover the fund. so I investigated my amazon activity, there was an email (auto) warning me someone has access to my phone logged into the amazon account. So I am dying to find out how this can happen and how to identify where went wrong and how to fix it and how to prevent it.

I received an email from Amazon advising me someone with access to my phone logged in my amazon account from Delhi India.

KiltedKim — do you mean I logged in using a link that was fake …

so what I shall do now to purge it?