If you feel like speaking your mind and being harsh, talk to your chapter executive board and advisers. You have a right to be heard if you feel you are being treated unfairly-- and calling those parties to a meeting moderated by your Standards/Personnel chairman is a way to start -- and will ensure the issues at concern are recorded. You should do this before you submit any formal notice to terminate your membership.
I'm sorry you made the decision to cancel your membership. This isn't "deactivation"-- you are terminating your membership completely in the sorority and you will no longer be a member-- you are no longer entitled to wear letters, any future daughters will not be legacies, you will not be eligible to recommend women for membership, nor will you be able to claim alumnae status or join an alumnae chapter. Nor can you join another NPC sorority. It's very permanent. Are you sure you can't work out this issue? If you really don't like the sorority, it is a moot point---quit.
If that is what you have decided is the best decision for you, then turn in your pin and do as instructed so the chapter can submit your cancellation paperwork to their national offices.
Your letter should include the date and something short and sweet a la "Please accept this statement as my intent to voluntarily cancel my membership in XYZ sorority. As of this date, I have no outstanding financial debts to the chapter. If you would like to contact me, please call xxx-xxx-xxxx or email
abc@123.com. Thank you.
Sincerely,
Signature
YOUR NAME"
This avoids any drama on paper. This also holds true if you should ever submit a letter of resignation at a job-- save the sob story for HR or an exit interview.