Two contacts combined?

Ok so basically, a few hours ago I used Siri and said 'tell mum .. [message]'.

Then a few moments ago I got a reply from my friend.. turns out he had received that message! I was then looking for the thread/conversation with my mum on my phone, only to realise it's no longer there. When I used the compose message button instead and selected her number, it opened up the conversation with my friend.

I then tried sending a message (to my mum) from my iPad instead, and after doing so I then looked at my phone to see that it had come up in the middle of a conversation with my friend.

I then tried to call my mum. I'm on O2 and usually before it starts calling it'll say 'free call' to indicate it's using my inclusive minutes, but this time it said 'bundle call' - I then ended it before it began calling.

I'm not sure what has happened and couldn't find anything after a quick search, but it seems as though two contacts have annoyingly been combined?! Has anyone got any idea how this would have happened, how to resolve it, or experienced this for yourself?

Also just to clarify; my mum does not have iMessage but my friend does. Both my iPhone and iPad are on the latest (excluding any beta) version of iOS. I've also double checked that none of their contact details overlap, and the problem still persists when turning iMessage off; it still says 'Bundle Call' before calling either of them.