What is the ruling on continuing to work in an interest-based bank for 13 years, knowing its prohibition, delaying leaving the job for financial gain, and disposing of the money and possessions acquired from it after leaving?

There is no blame upon you for benefiting from what was consumed by the money earned from working in the usurious bank—such as belongings, clothes, dental fillings, and so forth—because you are excused, Allah willing, as it was before the error of the fatwa you were following became clear to you, and you were not aware of the prohibition of this work.

You have done well by leaving that job, and you are not obligated to dispose of the belongings you own in which that money was consumed.

Beware of whispers and doubts, turn away from them, seek Allah's forgiveness, and seek refuge in Him from Satan.