Contextual backlinks helps seo the most. Google is way smarter than ever. I guess 1 contextual link from DA 15 site will beat those 2500 backlinks you bought.
1 more thing, do not try to opt for the cheapest backlink services. Backlinks that will actually help you, takes a lot of time and effort to build. Also it does not come with guarantee. So, go for the quality + value. 🙂