I’m an iPhone 5s user! With latest OS! Unable upgrade any apps from apple store nor buy any apps! It kept asking for my password and when I enter it, it will lead me to my payment section and back to entering password again! It never stop. Plz Help!!

I’m an iPhone 5s user! With latest OS! Unable upgrade any apps from apple store nor buy any apps! It kept asking for my password and when I enter it, it will lead me to my payment section and back to entering password again! It never stop and it kept asking for password, take me to my Payment info section and back to asking password! Irrittating. therfore, I have changed my password. But it’s the same again and again. I can’t upgrade or download my apps or any new apps in the store! Please Help!!