So do you intend to buy a separate ticket FRA-DME for the last leg? it seems like you will have to do so, having not shown up for your scheduled flight. Now you have forced a stop-over which isn't allowed according to the original terms of your ticket.
Would it be possible to upgrade your original ticket to a higher fare that allows a stopover by just paying the penalty and the fare difference. If so, that might be cheaper than a one-way ticket from FRA-DME.