I built my own website a few years ago for my own business. It was registered with IONIS 1&1, I Cancelled the domain as the business closed. The domain has been registered with a provider called Namecheap Inc and my old website content is displaying at the domain. I own all the content they are using, it was a photography website, I built it myself and all the photos are mine, the links are still active to my social media accounts. How do I get the content removed?
This is a legal matter more then a technical matter. Depending on the depth of your pockets and location use the DMCA and/or legal system to force them to remove your content. A threat claiming damages may be sufficient.
There may not be much you can do about stopping them from using your old domain name without expensive lawyers.
It is unlikely that Namecheap will help you without a court order.
That said this sounds quite unlikely. Are you sure your content is being used and you are not just seeing a cached version? The question would be how the new owner of the domain acquired your content and why they are sending it to your social media. Is there a copy of your content on the way back machine, or is the new owner in competition with you?