It is not right to pay the interest of loan by the interest money which you have received in your PPF account. There is no zakah on interest money. Hence you should calculate your zakah after deducting the interest amount received in your saving account. You should pay the loan off as soon as possible. Also keep on doing taubah and istighfar. Also recite the following dua for the repayment of loan in the morning and evening.
اللَّهُمَّ اكْفِنِي بِحَلَالِكَ عَنْ حَرَامِكَ، وَأَغْنِنِي بِفَضْلِكَ عَمَّنْ سِوَاكَ
Allah knows Best!
Darul Uloom Deoband