You are hardly the only member here who has ever done this. In fact, most of us here (that do not use stainless media/pins) have had to incorporate some method of dealing with corn or walnut media being stuck in flash holes or simply excess media that did not exit the case when pulled from the tumbler. It is a mandatory part of your reloading prep that once the brass comes out of the tumbler, you have to verify all media is out of the cleaned brass before proceeding.
I personally de-cap all of my fired brass before tumbling, then remove the cases from the tumbler and place them head-stamp up in some type of holder - a plastic ammo box works very well for this, then poke a small steel punch through each and every flash hole by hand to verify that I have no media left in the most likely sticking point of the case. Then, with all brass still in the ammo box with the necks facing down, I gently rap the box on my reloading bench several times to get any additional media to fall free out of the cases. Once I believe all media is knocked loose and out of the cases, I carefully lift the brass out of the box and place them neck up in my reloading block and shine a flashlight down into each case to further verify that they are absolutely free of debris.
I know of others that do roughly the same set of operations but then go the extra step of blowing through each case with compressed air.
Simply put, this is an exceptionally common problem, no matter what size media that you use, so don't worry about where you bought it. If it cleans your brass well, you have what works for you. I'd just modify your process to clean/tumble your brass after removing the spent primer and then verify that all corn is out of each piece of brass before moving to your next step.
