As to the temperture settings then look at it like this number 1 is the warmer setting and 7 the coldest setting.
So if you have it on 3 this is roughly around the -18 degrees c mark which is normal running temperture of the freezer.
So turn the dial down to 2 and see how it goes. But if its still getting too cold in there and the food is rock solid then its going to be a fault with the thermostat which in this case the thermostat will need to be replaced.
Sorry i dont know what you mean by the thermostat dial showing it as 5,10,13,20. As looking at the service info on this it just shows the dial going from 1 to 7 but missing some numbers. So the dial actually shows 1,3,5 and 7 with a dash inbetween each number. I take it then yours doesnt show that?
But if the dial is set to say 2 then this is about -17 degreess
Number 3 is about -18
4 is -19 and so on.
As to replacing the thermostat then im afraid it does need to be pulled out. But only a few inches so you can remove the cover on the top of the freezer just above the dial as you can replace it from there.
Glad to hear its sorted and thanks for letting me know.
If you could remember to rate the answer that would be great.