Gamertag/ Account hacked

Hi guys,

I'm posting on behalf of my dad who's 73 and getting nowhere with his Xbox one. Yes he's still a gamer.

It all started about 3 weeks ago now when he switched the Xbox one on and saw a new gamer tag on his console. This was asking for a password but it had some letters already inserted as a kind of prefix.

He contacted Microsoft support who sent him some guidelines to create a new gamer tag so they can merge his files. He did as he was told and they removed the password protected gamer tag and created him a new one.

Frustrating for me as I couldn't see what was going on only listen on the phone. So long story short, his original gamer tag/achievements have all disappeared and he's left with an Xbox live gamer tag. He never used his console online although it was connected
to the internet for updates etc. He was told to change his primary email which he did . He's now changed it back in hope to restore his original tag but to no avail. This has now been going on for about a month.

So my question is... Is there any way he can retrieve his original gamer tag and all his game saves etc? We have now looked everywhere on support and had no joy with it and found ourselves going round in circles.

Any help would be appreciated so he can get back to gaming.. Cheers.

:)