How can one repent from backbiting and consuming usury without returning the money or apologizing to those slandered, especially with a hardened heart, arrogance, and stinginess, and does this indicate sins?

If you submit to Allah the Almighty, Allah will forgive all your sins and erase all your previous evil deeds, as He, the Exalted, says: {Say to those who disbelieve, if they cease, what has passed will be forgiven for them}. Your feeling that your sins are immense is a sign of goodness and the beginning of guidance. Islam demolishes what came before it in terms of sins; rather, it transforms evil deeds into good ones. Usurious wealth acquired before Islam becomes lawful for you after your conversion to Islam, and seeking forgiveness for those you slandered suffices for you. Hasten to embrace Islam by uttering the two testimonies of faith and acting upon its laws, so that you may attain happiness and salvation in this world and the Hereafter.