It was Serbian, actually.
The closest to “Jebem ti boga” in Bulgarian is “tvoita vera (poganska)” lit. “your (pagan) faith” and the action part is withheld entirely (but implied, mostly).
Also, fuck your heart is too poetic. In Bulgaria we say “ebem ti droba” lit. “fuck your liver”. It’s a friendly colloquialism like “Hey, how are you doing today, friend, da te eba u droba?
And we most definitely won’t fuck or piss on someone’s soul, although we would on your brain as in “da ti pikam na mozaka”. Which expresses ambivalence about someone’s mental acuity, rather than general offense against the person.

P.S: Stay with me, you’ll be speaking Bulgarian in no time at all.