oh wow. bad advice.

First: no ferrules.
Second: the head didn't seat properly when first installed, this jammed it under pressure and the metal end is likely deformed and wedged.

Try: 1. shorten the cable to a 2 inches, try tapping the end of the cable with a plastic mallet.

2. Remove the ergolever, place in freezer for an hour, then heat it up slightly near a heating vent. Do this for a few cycles. The hot/cold cycles will expand the metals at different rates.

A bit of grease on the cable end when installing helps avoid this.