You should contact the support team[support.ubi.com] regarding this account issue!
I also play quite a bit of Mute and also run the MP5K. I think it could use a tiny buff but otherwise, it is fairly solid. I personally am not a fan of shotguns so I typically do not use them, but I did see some players the other day absolutely pop-off with his shotgun.
The idea to have Mute's jammers be deployable on walls would be really cool! Mute could use a little bit of love :P