What's wrong with you Harry? Your sentence is completely wrong, it means: "Oh I had lost contact with her soon." That doesn't make any sense. (before long = soon). Soon never comes with the past or past perfect. If you want to learn, be a flexible learner. "We learn from the cradle to the grave". By the way, Anglika's sentences are correct.
Aamrym, may I suggest that there are more gentle ways to point out your disagreement than with the words you have chosen?
While I disagree with Harry that there is anything wrong with Angika's sentence, I do support that "I had lost contact with her before long" as a correct sentence as well. It means "Before much time has passed, I had lost contact with her."
To use soon, you'd use it like this: I had soon lost contact with her. It would need to fit into a running narrative.