Quantity discounts - problem with appearance in PrestaShop 1.7

Hi, I just bought the Products list quantity discount update to 1.7 and it doesn't work. I used fot 2 years with no problem. Can you help me? I previously used 1.6 version

As i suppose fact that you previously used 1.6 version is the source of the problem.

Please firstly do this:
- go to back office of your shop
- uninstall the current version of the module (not matter what version you currently uses). During uninstallation select option to "remove the module": https://i.imgur.com/qJanGYs.png (this is an example)
- then download correct .zip file (dedicated for prestashop 1.7) of the module
- upload and install it in your shop

Then, depending on theme:
- open configuration of the module
- depending on your theme select displayProductListReviews or DisplayProductDeliveryTime position in this option: 

If your theme follows prestashop standards and guidelines the position displayProductListReviews is a correct position.
If module will not appear in your shop's front office it might be required to review configuration page of your theme - there is a possibility that there is an option to activate / deactivate availability of hooks (including displayProductListReviews hook).