Statutory Redundancy Pay

In a bit of a pickle at the moment and can't find a straight answer anywhere, wonder if anyone can advise.

I was made redundant around 6 weeks ago, the company has gone into liquidation so have had to claim my redundancy pay off the redundancy service.

I've had my settlement email today and its less than half of what I was expecting.
I worked in sales and had a very low basic, less than minimum wage. I earned commission every month though which meant I normally picked up 2-3 times my basic wage. My redundancy pay settlement hasn't taken into consideration my commission - it was in my contract. I can't find a clear answer anywhere online - should the redundancy service take into account my commission/bonus when coming to a settlement? I know its capped at £525 a week however my average weekly wage including my commission was more than £525 a week so I was expecting to receive the maximum.

Please note I have asked the company handling the liquidation of my old employer and she has stated they don't include commission - however looking on Google I've come across a few websites saying that commission and bonuses should be included and they should base it on an average of the 12 weeks leading up to the day I was made redundant. The rep from the liquidator sounds a bit dim to be honest so I don't really want to take what she says as gospel. I'm basically trying to find anywhere in black and white that says whether it should be included or not. I can't find anything on the GOV website. Also the GOV calculator online just asks for weekly pay, it doesn't say basic pay.

If they don't include it should they base my weekly wage on what the minimum wage equivalent was for the hours I worked?

Thanks in advance for any help/advice.