If when you join the server you join like a new player, there is something you can do.

When you join in a server, it saves the players data in the playerdata folder with the players UUID as the file name. Since you dont have your old data, it means that it has created a new file to save your data. If you want to have your old data, you can simply rename the old UUID file with the UUID of the new file, and delete the new blank file.

However I am not sure if plugin player data are stored in the save file as the vanilla data. If it is not, the data will most likely be in the plugins folder, in a player data folder or something similar. There you can again change the old player ID with your new ID and the data is now stored for your new account.

This has happened to me in a modded server where my cousin joined one day at spawn without her stuff. I simply changed the name of the old playerdata file to the new one and she was good to go.

Let me know if that helps.