ことだから・ものだから: the difference
ことだからN2
Meaning
Knowing
Past papers
Example
神様のことだから、必ず助けてくれます。
Knowing God, He will surely help us.
ものだからN2
Meaning
Because, The reason is
Past papers
Example
郊外に家を買ったものだから、通勤に２時間もかかる。
Because I bought a house in the suburbs, the commute to work takes two hours.
How to tell them apart
「ことだから」: a guess based on knowing a person. A person (〜の) comes before, a guess after.
「ものだから」: an excuse for yourself, followed by something that already happened: 「電車が遅れたものだから、遅刻した」 (The train was late, so I was late).
The two are often used as wrong options for each other.