Not true. In classical general relativity singularity have 0 size.
Any other theory to avoid 0 sized singularities (LQG, string theory) has not been accepted and that's actually my point: true hard singularities are probability due to our theories not being complete and likely something else happens. However, you can't claim you know singularities have plank volume because no one managed to quantize spacetime in a coherent theory that explains everything we observe.