How can one get rid of obsessive thoughts that involve insulting the Divine Self and the Qur’an, and cause a constant feeling of guilt and a rejection of good deeds, which hinders the performance of acts of worship?

This is a manipulation from Satan; do not succumb to it, and seek Allah's help to repel his whisperings.

Among what will help you:

1. Know that Allah does not hold one accountable for what one thinks to oneself, as long as one does not act upon it or speak of it.

2. Persist in the remembrance of Allah and the morning and evening supplications.

3. Seek knowledge and attend gatherings of scholars.

4. Recite the Qur'an over yourself, or present yourself to a righteous person to recite over you.

Do not surrender to delusions, and your fear of sins indicates your reverence for the sacred limits of Allah. If you abandoned prayer, you have done wrong; so repent with remorse, cessation, and a firm resolve not to return to it, and make up for what you missed. If you fall into a sin, know that its cure is sincere repentance, for "the one who repents from sin is like one who has no sin." Allah is Forgiving, He forgives sin, so perfect your repentance and have a good opinion of Him.