every permaban is manually reviewed by riot employees. they go through your chat/account logs manually and decide whether to ban you or not based on that. chances are that you've been extremely toxic in the past, have boosted someone or were boosted yourself, or meddled with the rp system. :3
Toxic = No. I’ve been playing since season 1 and rarely type, never had a warning or chat restriction.
Boosted = Nope
RP System = Apparently it may be due to a bounced payment but we can only wait and see