My cell has a permanent image of a square magnet

Here's one thing you can try: Take the cell out of the housing and place it in an oven set at 95 deg C. Heat it for about an hour. Then after it cools down, place the cell on a smooth flat surface (like a table top).
Use a soft cloth on the area where the square 'burned' area is. Rub in small circles around the area while pressing hard downward.
Do this a couple of times. If the square burn is still there after a couple of tries, then put the cell into a padded envelope and send it back to: Ferrocell USA, 739 Route 259, Ligonier, Pa. 15658 USA and I will repair or replace it no charge.

Next time you use the cell, don't leave the magnet in one position for more than a few minutes at a time.