I got PERMABENNED and i did literally nothing

My account got banned on the 21th of April for the following reasons: Your account: karkadan93 was banned due to the use of malicious 3rd party programs or modifications to your League of Legends client. The only programs i used were: SkinPreview where you can use custom skins, and replay program. When they replied to me they said I was using exploits but they didnt want to inform me which programs I was using.

So to keep it short: I never used scripts or anything alike. Keep in mind this is my first and only League account where I also spent a lot money, so I dont know why I would even risk using scripts or cheats. I never heard of someone banned for using custom skins and I have litereally not been using anything else - I would love some insight, since my account is currently perma banned and I have no clue why and have no other way to get in contact with Riot.