Discount remains when removing item from cart

Hello

We have a problem in the web cart that we need to solve.

We currently have a volume discount active for 3 or more items (but we have one category excluded).

If we add 3 products to the cart and one of the category that we have excluded, everything works correctly, the 3 products have their discount and the one of the excluded category does not.

The problem is that if we eliminate one of the 3 products the other 2 continue with the discount. This only happens if there is a product from the excluded category in the cart.

How can we solve it?

Thanks

The page I need help with: [log in to see the link]