All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
Congratulations to you for the guidance and adherence to the true religion that Allah the Almighty has bestowed upon you. We ask Him, the Exalted, to keep you steadfast in His religion.
As for what you have inquired about regarding these debts, if you are certain of your debts or you think that most likely you did not pay them off, then hasten to pay them back to their owners to the best of your ability. Don't wait for them to contact you; instead, strive to clear your liabilities, and if you are unable to reach the owner, give the amount of the debt in charity on his behalf. If you don't know the exact amount, estimate it to the best of your knowledge. There is no distinction in these rights between a Muslim and a non-Muslim.
Allah knows best.