Answering these questions would add context to aid in obtaining the most appropriate or best wording:
Is/was this a literal (i.e., monetary) debt, an actual loan (casual, or formally documented)?
Is/was the debt in the form of money or property because you damaged property (intentionally, or by accident/due to carelessness)?
Or is/was it more in the figurative sense, as a moral obligation ('debt') incurred due to something you did or said that was offensive? Or, in the positive sense, is/was it the proverbial 'debt of gratitude' due to some act of kindness by the other person preventing loss, injury, or embarrassment to you?