Trooper Fresh Water Tank won't fill

In May of 2023 I purchased a VW Trooper, with Reimo top, which was manufactured in 2011. With winter approaching I drained the fresh water tank using 'both' drain taps and now I find I can't refill fresh water tank.
This is my first camper/motorhome with a Whale system and I must admit I am not a fan of the Whale system so far
How on earth do I gain access to the water pump , pipes etc. All I can find is an access hatch just big enough for my hand to reach through which is located in a under sink cupboard at floor level.
Any help or advice is much appreciated.

Hi Pop Top Robert, just filled up the tank on my 2014 Trooper which I think is pretty much the same. Connect the Whale filler pipe to the van and tap / pitch service point. The van end needs to be pushed fully home. My previous Symbol sometimes popped out. Turn on the tap and the van control panel and away it goes. It takes about 20 mins to fill. I normally walk away and leave it to fill. It will cut out once full. 
I haven't tried the barrel filler but did use it on a previous van. Same procedure as above but with that pain of lugging a barrel around. 
The tap in the cupboard is the winter drain down for the hot water tank. 
I haven't touched the pump on the Trooper but had to change one on a 2011 Symbol that used the same submersible pump. There should be a large round inspection hatch on the base of the tank. This unscrews (with a bit of effort and some large grips) The pump can then be pulled out. The cable connections are outside of the tank where the water pipe exits the tank. 
The other part of the system that can be fun is the pressure switch. There are plenty of post on the forum about adjustment. On my Trooper it's located under the work top next to the sink. 
Hope this helps.
Pete

Thank you Pete for your reply.
I will try this .
I hope it is the whale filler pipe, I have noticed that it does partially pop out (the top part when plugged into the van).
It has been working fine, until I drained the boiler tank. I have noticed that when I drained the boiler the drain tap it seemed to become lose, so maybe it has been loosened , and if so it will not pull water into the tank but air instead. So I will try to tighten (only finger tight because fittings are plastic and may be a little brittle with age).