Same domain but different websites showing on PC and mobile phone

Question

Here is the thing. I had an old website uploaded to a registrar(let's say registrar A), and I recently built a new website uploaded to Namecheap(a new registrar) using the same domain of the old website.

A strange thing happened when I wanted to redirect the domain to my old website by changing the DNS in registrar A(changing the DNS from the one that Namecheap provided to the default one that registrar A provided): the website showing on my PC was still the new website but the what showing on my mobile phone was the old website. After several hours, when I changed the DNS to view my new website, what showing on my PC was the old website but new website on my mobile phone. HOW???

Answer 1

Sounds like a DNS propogation: https://www.namecheap.com/support/knowledgebase/article.aspx/9622/10/dns-propagation--explained

Flush DNS https://www.whatsmydns.net/flush-dns.html

Hope this helps