もの / もんだから
Usage
(V / いA / んA / N) + もの / もんだあから
indicates the reason or cause of something
is sometimes used when an undesirable event (Y) has occurred, to justify it or give a reason for it in order to deny responsibility and exculpate oneself.
Examples
急いでいたものですから、鍵をかけるのを忘れてしまいました。
Was in a rush, so I went and forgot to lock up.
すみません。出かけようとしたら、電話がかかってきたものですから
I'm sorry; the telephone rang when I was about to leave
Good to know
ものだから in the same way as から and ので can't be used to indicate an objective cause or reason