Up to you, only advice anyone can tell you at this point is to message Nitex on discord as he answers more frequently there than the support page here.
Note that the system is constantly learning, it probably won't ban you immediately if you sell an item for op price via agency the first time, but if you keep on doing other things that the system deems as suspicious, the accumulation would certainly get you auto-banned. None of us know the specifics of RMT detection, you'd really need to dm Nitex on discord and prove your case.
See this article:
Browse down and go to RMT detection, this is where this system was first mentioned as well some info about it. Of course, to prevent bypassing the system, Nitex will likely not release the specific parameters used by the RMT detection, but an example would be selling a trash item for 30b in agency (as stated in discord) - a red flag for real money trading. Just dm Nitex on discord to appeal your case if you really didn't do RMT.
You'd have to ask dm Nitex for the specifics. There is a system that monitors all dil flow via agency, direct trades, personal shops, and even dils dropped on the floor. It must have flagged a specific activity you did as suspicious, hence why you were banned. No warnings for rmt, as far as I know.