That's stupid for two reasons:
1) You deny the authenticity of Paul's writings without giving any reason to.
2) Paul is a Jew, and Jews are monotheists.
Consequently, unless you believe the scripture is silent on monotheism, then you must confess that such false teaching is damnable, whether you like it or not. If I believed that people will go to hell for believing that there are three in the Godhead instead of just one then I would also have to believe I would go to hell
I assure you, hell is where all those who deny the Trinity or who are polytheists go.
That’s stupid for two reasons:
1) You deny the authenticity of Paul’s writings without giving any reason to.
2) Paul is a Jew, and Jews are monotheists.
We might assume Paul told them at another time but we do not know, if he did not then it is false teaching to say some one is going to hell for believing in the trinity which is three.