I can't believe you count the calories in benefibre, this should only be used to top up your fibre intake not be it entirely.
Also you know that 800 calories is not enough, 1200 should be about the least amount you intake. What your doing is not healthy or nutritious, your get run down, your gums will suffer badly, face will probably become spotty and as for internal damage who knows.
Why don't you up you calorie intake a bit by adding some vegetables and fruit, you'll probably find by eating a bit more you'll actually lose more weight & fat because your body won't be in starvation mode like it is now.
Try 4-6 smaller meals a day to keep your systems going and stave off hunger. Protein is filling and keeps hunger at bay for longer so up this along with fruit & veg.
This is what I am currently doing but I am getting lots of protein, fruit & veg inside me