Basically you must demand to have your logs verified, tell them you are 100% sure you didnt sell her neither used her as upgrade for another girl, but if they can confirm this with your logs then you are done, you must only accept proves that you sold her/used her as upgrade, not a simple "i think you sold her" that is bs for a customer service support

A lot of times (in my experience) with the JP version is that after every server maintenance and event reset, your cookies also get reset. This means that your settings default back to zero. In the case of your locked characters, they should remain locked, however, the order they appear may change.

Now, here's the deal breaker: if you were found to cheat, using a 3rd party cheating tool or an auto-play tool (where you can go AFK and have that software play for you), then you aren't going to be able to get your case through. And any issues caused by using illicit 3rd party tool is not Nutaku's responsibility, since you acknowledged to the 3rd party tool that they cannot be held responsible, either.

I'm not saying that you did, but there's many variables here for the others to consider, before taking sides on this issue. I don't know you, afterall, you're just a random Joe on the internet, and no one really knows your situation without having to live alongside you. This includes having siblings or other people in the house screwing with you, or having your account hacked, etc.