No use in paying for priority

I just boarded a FlySafair flight to George. I pay extra for priority boarding so that I can get on the plane early and make sure I have space for my hand luggage. I had a biggish back pack. Then when other customers come on with two bags and they run out of space, I am told to put my back pack under the seat in front of me so that other passengers can put their suitcases in, because mine is “only a back pack”. I am a large guy and to not have space for my legs is a major problem for me. The crew member was also rude to me. Not a fan.