JP,
More power to you. May Allah bless you with strength in prayers.
HoWEVER
We need to be very careful in calling someone PAGAN just because the person is looking for an answer in the physical nature of things.
Why? because both physical nature (meteorology) and spiritual nature (prayer for rain) are governed by the rules of Allah.
Thus exploring and learning about physical nature is as important
as
believing in spiritual nature.
Instead of arguing with him, you should apologize for not trying to understand his point of view. Not only that, you labeled him as a pagan. That’s worse thing to do to any person let alone a Muslim.
No one should claim that they prayed and were able to move the rain schedule. And I am sure you never meant that.
Instead when we pray, we simply ask Allah for his mercy. And it is his mercy and his alone, to award us with something, or he may not.
So keep on praying without judging other people.
Best wishes.