Umar, softening of the heart is a long process that requires faith in Allah (swt). Tawbah literally means to return; so return to Allah (swt) with full faith that he will forgive you and pray to Al-Mujib (The Responsive) to soften your heart.
Here’s a hadith that encourages making tawbah:

A man asked Abdullah ibn Masood (ra) about repenting from a sin which he wanted to commit but did not commit it. Abdullah (ra) turned away from the man and then turned towards him with his eyes weeping and said: “Paradise has eight entrances, all of which open and shut except the entrance of tawbah. This entrance has an angel guarding it so that it does not shut. So repent and do not despair.”

I agree with Allen that the immediate remedy should be to stop sinning with the intent to never sin again, and to readily do good deeds. Inshallah your heart will soon be a qalbin-salim.

Brother I feel the same way,

you just have to keep trying and tell Allah that your sins are so much that you can’t make a sincere tauba. Just stop sinning immediately insha’Allah and try your best to do good deeds. Insha’Allah the deeds will soften your heart more and you will be able to make a better tauba Insha’Allah. If you have your mom near you, then try to make her happy and kiss her and think of the mercy of our Rabb

A book I highly recommend is “Purification of the Heart” by Hamza Yusuf…great book.