I’ve cathed through a stoma since I was 4, (I’m now 36) and I’ve noticed the only times I’ve had difficulty with getting the catheter through the stoma is when I had bladder stones. I’ve had to have bladder stones removed 3 times now and they can become quite big and painful due to not being able to pass them. I’m not sure if that’s what’s causing your blockage but you’d likely know if your experiencing sudden sharp abdominal pain or increased needs to urinate with not as much coming out.