How have you been ' driving ' them in ?
Steel faced hammer on steel dowel pins may have blossomed the ends enough that they will not go in...
Sometimes it is better to use either hardwood , like oak, or soft metal , like brass, to protect the part being hammered....

How long were the dowels to start with ?... the amount sticking out seems very small... if they were over an inch in length to start with you might just grind off what you can not get driven into the hole....