What is the difference between "thaan" and "nee"?

I always used "thaan" to address strangers or acquaintances. I just can't bring myself to call someone I just met (or even a colleague at work whom I don't consider as my friend) "nee" from the get go. Recently, I learned that calling someone thaan/ thante is considered rude, while I thought I was just being polite/ respectful. Should I just stick with names for all conversations in Malayalam now (feels really weird)?