Same problem with with my Experia M4 as Cazycarey . Tried an email to customer help but no reply yet. Probably get the same response as well, so it needs everyone who has has this phone and problem with storage to contact them and maybe then we can get some action to resolve this.
Welcome to the Community, I'm sorry to learn about the problems you're experiencing at the moment.
I've been able to have a look online and can see quite a few similar threads, there's some good tips and tricks to try [here]. What do you see when you try to move your applications to the memory card?
If you've not tried it this way already, I'd recommend giving it a go:
To move apps to the memory card
From your Home screen, tap .
Find and tap Settings > Apps.
Select the app that you want to move, then tap MOVE TO SD CARD.
Just spoken with Virgin support and they have set up a complaint case no re my Sony Xperia Aqua M4 the Android OS is taking up excessive memory apparently this is an issue with all the M series phones. I have been assured of a reply within 24 hours. Let see.
Everyone with this phone should do the same as Virgin media do not appear to be addressing this issue maybe Mr Tom Mockridge the CEO should be made aware . I will certainly communicate with him if there is no satisfactory outcome tomorrow.
There needs to be some form of compensation from either or both Sony/Virgin for allowing this product which is not fit for purpose on the market.