Also some people encounter battery drain problems since the upgrade to A13 (like myself, see FP4 battery life got worse after Android 13 update - #209 by Lars_Hennig ). Can you check the root cause for your battery drain?
Feeling you have been cheated is something nobody will be able to change, but together we could try to find out if the battery drain issues on the FP4 all have something in common or not.