In short, a free service is being replaced by a paid service, primarily due to folks such as you rusing and abusing the free service. Ten domains is abuse - period. And then you wonder why the replacement service (such as it is) is structured the way that it is. It's three pounds British per month, and is not as wide open to rusal and abuse as the old service.
Did you expect Microsoft UK to stay stupid forever?
To claim ten domains is abuse is silly - period.
MS set up this service for vanity domains and very small companies that wanted free email while MS got to shower them with ads. Most of all, they did it because Google was doing it. When Google got out of the free domain hosting, it was just a matter of time before Microsoft would. Combine that with the fact that most people don't see the ads anymore thanks to Outlook and the outlook.com app. So MS started losing money for a service that no one else offered.
It wasn't abuse that killed it, it was a lack of revenue and lack of competition.
You can find cheaper hosting at other places, your ISP might even have hosting included.
I had 5 domains that I ran, most of them with 2 addresses each and mostly for family members that wanted their own domain.