This issue arises occasionally.  We can help.

There are several reasons why you may not have full control of your domain name.  Often that’s for the perfectly valid reason that you have delegated domain name management to a third party. The reason for using a third party is because some end-users will struggle with the whole issue of domain name management, DNS and Nameserver setup, keeping the registration details up to date, having the know-how to make configuration changes.

In the early days of web sites individual designers would routinely register client domains in their own name, not with any ill intent but to keep things simple.  Clients did indeed get confused when they received separate invoices for domain name and hosting (and possibly other related services) from different organisations, an issue compounded by the common “domain name renewal” scam mails. We found we would get calls from clients to say “we paid you for our web site last month and now another bill has arrived…”
So there was good reason for the host to manage domain name renewal too. The problem than arose that a one-person web design company was a “single point of failure”. We recovered a few web sites and domains in  circumstances where the designer was impossible to contact, maybe unwell, simply no longer interested and uncooperative, maybe even having lost the relevant details themselves or in a couple of cases had emigrated.   The most extreme instance was a business with their entire stock control system on a private web site they could only access through (password protected) web-page queries. The web host would only deal with the original designer who could not be contacted. We had to write program code to fire thousands of queries at the database to display each stock item on-screen then run a screen-scraper to capture that data, rebuild the database and rebuild the database query programs. 

I’ll give a real-life example:
Many of our clients hold more than one domain name maybe example.co.uk, example.com and example.uk In that scenario their actual web site will probably just use one of those names. The best choice would be  example.com while example.co.uk would automatically redirect UK users to example.com and example.uk would go nowhere but is held simply to prevent a third party using it to the disadvantage of the holder of the other two variants.
Our client changed their email address but only updated it in respect of example.com Renewal reminders for the UK variants were sent to the obsolete email address and so were not actioned. The website was working fine at  example.com so it was several months before anyone alerted example.com that example.co.uk was no longer redirecting.  That meant anyone looking for example.co.uk would decide the company was no longer trading. The registration had lapsed and example.co.uk was back on the open market.  That was a stroke of luck, as dropped names are usually spotted and bought by speculators hoping to sell back to the original owner for a very substantial price, in the mean-time using it to host advertising content or worse.  In this instance I guess the speculators decided that the name was too obscure to generate any revenue for them. We simply re-purchased the name from Nominet.

Your domain name may have been registered at any time since the early 1990s. The person who registered it may no longer be in contact or, as above, the registrant details may have become out of date.

.com and .uk names are provided by two different organisations, updating one does not update the other. Both have ways to recover control of domains but for obvious reasons they are a bit involved, the aim being to prevent malicious persons gaining control.