They are more than likely doing this with PBNs. They block third party crawlers so the likes of semrush and ahrefs are unable crawl so you cant really see how many links those pages actually have using common backlink monitoring tools. They rank because they have high domain authority as a result of all of this. A website with more domain authority will rank above you because Google considers it a more trustworthy website.This can often be a difficult battle in the SERP pages but it is a fact of life unfortunately. You will need to put effort into producing more quality content for your website and the rankings should improve over time as you obtain more links back to your site.