we did this 1 month later. No effect.

We did a general 301. Not a product specific 301. Mistake?

301 redirects by page for sure 1:1.

Plus, How is this linked to shopping carts?

well, website.com/product=11 became website.com/myfavoritejeans

This is called product pages, cart will be website.com/my-cart or something in the like.

so, should we have done a 301 for every product?

Seems to late now.

Yes 301s for each products to new page is ideal.

I don’t do SEO for other companies, but I can take a look at your analytics data, and make a couple of suggestions if that can help. PM me.