Thank you, but I'm not sure this is actually what's happened? My post count does indeed seem to be set to 0, but all of my posts still seem to exist, and can be easily seen by checking my profile. Being able to see my old posts listed via my profile might be something only I can do - I don't have the means to check that myself - but I can confirm that even when logged out, my old posts can still be seen if you're already looking at the relevant pages.
I can confirm that I as a regular user can also view older posts from you still.
You could message an admin and ask them to delete your whole account. The posts will still exist on the forums then, but it will look like they were made by "Guest", and won't be tied to a profile. You could then make a completely new account. This has been done relatively smoothly in the past at least, but I am not sure what staff policy is these days.