I'm sorry to hear you are having trouble getting your name removed. If you did not receive an official letter from the Church, then your name has not been removed. In reality, I don't think they really take your name off their records, they just move it to a different file. They would say the reason is in case you ever wanted to reapply for membership. I personally think they just want to keep track of "apostates."
I would write a brief letter and send it to the Membership department. Something like the following (please feel free to modify it):
Dear Mr. Dodge or Records Assistant;
As of (fill-in-the date you first wrote your branch president) I terminated my membership in the Church of Jesus Christ of Latter-day Saints by writing a letter to my branch president (Bishop So-and-so of the Such-and-such Ward). This was over three months ago and I have yet to receive any confirmation from Salt Lake City. The bishop will not take my calls.
Please remove my name from the records immediately and send me a letter stating that my name has been removed at my request. The word "excommunication" is not to appear in the letter or on my records. I am prepared to take further action if my request is not promptly acted on. I have sent a copy of this letter to my branch president and stake president.
Sincerely,
(Your name)
(Address)
I hope this helps! Please keep me informed. The address of where to send your request is below. Be sure to send copies of your letter once more to the Branch and Stake Presidents.
Member Records
50 E North Temple, Room 1372
SLC UT 84150-5310
God bless you H___! Keep in touch!
Tracy