how do i stop the predictive typing suggestions
Prediction and autocorrect are two different features. What you are describing is autocorrect. You can disable autocorrect by following:

Settings > General > Keyboard > Toggle Auto Correction off. 

The issue you are describing however sounds like it stems from you accidentally entering a password into a plain text field which has been added to the autocorrect dictionary. You might try resetting the dictionary first to see if it resolves your problem:

Settings > General > Reset > Reset Keyboard Dictionary.