What can I do to stop this? Any help would be greatly appreciated.
Nothing. You can do absolutely nothing about it. Sorry, but it's honest truth.
It may just be a case of someone impersonating your email address but sending the mail through non-hotmail servers, which is very common.
It may be a case of someone having guessed your password and hence using your account for spam (less common), in which case you should obviously change your password (a good thing to do once in a while anyway).
It's one of the downsides of using free webmail services such as Hotmail. They're the most heavily targeted places by spammers.
Long term answer is to swiftly make and put in place plans to change your email address.
You should also email any messages you are aware of to
[email protected] ..... but don't expect them to fix anything.