Is an individual's performance of Hajj, followed by their return to watching pornography, listening to music, and masturbating, a sign that their Hajj was not accepted? And what are the practical solutions for getting rid of these sins?

The sign of an accepted Hajj (Hajj Mabrour) is the pilgrim's diligent obedience to God afterwards. If he plunges into disobedience, that is a bad sign. However, the opportunity for sincere repentance (Tawbah (definition) Nasuh) is still available, so he must abandon sins before it is too late and before a bad ending.