Is he who established a da'wah page with music, and it was stolen from him and used to spread rumors, rewarded for those who were guided by it, and does he bear the burden of the music and what was published thereafter?

Whoever causes good will be rewarded for it, even if he did not intend it. Similarly, whoever commits a sin and causes its spread will bear its burden, unless he repents and strives to remove its traces to the best of his ability. Therefore, the questioner is rewarded according to the benefit of his page. As for repentance from the sin of music, it is sufficient for him to strive to delete the page and request its deletion from those involved in it. The sin of whatever the page-stealer publishes falls upon the perpetrator, not upon the questioner.