How can one purify money from accumulated bank profits, without remembering the original deposited amount or the extent of annual increases?

If dealing with the postal visa is based on usury, then it must be stopped, and the money withdrawn. The original amount and the added amounts must be precisely determined, and anything in excess of that disposed of in charitable ways. If you give out 8% of the total money, you will be absolved, as an educated guess is acted upon when certainty is unattainable.