The "local matter" letter is de rigeur. Now you just wait out the 30 days the local folks have to process it, and you should get the "Per your request, your name has been removed..." letter.
I wouldn't get too worked up about it. Go buy some bubbly and pop the cork when your confirmation departure letter shows up.
I am known, because I actually became active in my new ward approximately a year ago, when my wife converted. I like the guy, but I hope he doesn't try to visit.
Or send it back with: I'm not stupid. The law says I've already resigned, the moment you received my notice. I do not wish to receive any contact whatsoever from your representatives other than a letter confirming my resignation.
I essentially did this. I basically wrote that it was irrelevant that they considered my name removal "a local ecclesiastical matter". I had written the church membership headquarters of my resignation and I expected to get confirmation within 10 business days per US laws. They of course did not comply, and I did not expect them to, but I wanted something in writing to beat them up with if it came to that. As it was, I got the official letter not much later than 10 biz days.
The excuse will be that he must be sure you understand the eternal implications or he must be certain you are who you claim to be. Yes, they actually say some exmo might try to impersonate a TBM and mess up the record. LOL
If you want to eliminate this final contact, you could phone or email the bishop and tell him you're serious about resigning and you won't tolerate this last intrusion on your time and patience.