Denied boarding due to full train and delay compensation claim

My Virgin Trains train (UK) was cancelled, as were two others in the same direction.
With the next available train, I would have arrived at my destination with 40 minutes delay, but as I arrived at the platform I was denied boarding because the train was full.
The train after permitted me to board (I had learned my lesson and ran in order to board before others), and I arrived with 90 minutes delay.

I suppose this means I am entitled to a 100% refund of the single fare, but how do I claim this?
There is no place for comments in the delay repay form, and they're likely to consider my delay was 40 rather than 90 minutes, as was the case for many others booked on the same train as me.
I have filled the delay repay form and then e-mailed Customer.Relations@virgintrains.co.uk with the additional information.
Is there anything else to do under those circumstances?

Are there any regulations about rights in case of denied boarding due to overcrowded trains?
Does "train was overcrowded, passengers left behind on platform" get registered in the company's system?

Edit 2017-10-20: Virgin Trains West Coast have processed my claim and state I am only entitled to a 50% delay repay, but I have replied describing the situation, and that I believe I am entitled to a 100% refund.

Edit 2017-10-23, morning: After my complaints, Virgin Trains West Coast have promised to “get this looked in to and rectified for you”. Let's see what happens next.

Edit 2017-10-23, evening: I have now received confirmation that I will receive the full refund.