carrentals.com low rental, high extra charges manchester, Internet

We rented a car in Lanzarote, Can. Isl. through CarRentals.com. In Europe it is common practise to return it with a full tank and if not they charge you for the top-up.
The car was o.k., of course we were forced to take extra insurance, because it turned out that the ADW was not an ADW, but so far so good. After 2 week we delivered it at the airport wit a full tank.
After our holidays we noticed that on the collection day of the car Euro 110 was charged to our cc.
This wa when I rented s specified as full tank, extra insurance and administration costs.
We have sent them the petrol bill showing date and litres, but he just answered that it was mentioned in their general term. I know that this is common practise in the USA, but this was extra pointed out to me by he Hertz official when I collected the car in Florida last year.
I feel cheated both by the extra insurance and by having to pay twice for a full tank.
They should inform their customers better.
This is an easy way to show great rates.