If your BatchNorm layers are set to affine=True, they have the weight and bias parameters (gamma and beta in the paper), which are initialized with some values. If you don’t train these layers at all, both parameters will stay in this initial state.
If you still want to standardize your activations with the running_mean and running_var, I would suggest to set affine=False and test it again.
Let me know, if this helps!