stop feeding so much!
the snail population will only multiply if there is enough food to support it, so the fact that it has grown means significantly means that you are feeding too much so the first thing to do is cut back to stop the problem getting worse.
supposedly if you put a piece of lettuce or cucumber into the tank overnight it'll be covered in snails in the morning and you can remove it then, although this method gets mixed reviews.
personally i would just say take them out by hand, it'll probably take you a week or so but just take 10 minutes each day and pick out all the ones you can, this combined with a sensible feeding regime should get rid of them and stop them coming back. you'll never eradicate 100% of them but you should be able to get it much more manageable