Unfortunately, they aren't much of a help. I'm in a similar situation, didn't receive a 48-month extension letter. I already sent two e-requests about a missing form (no response), called 4 different people (Tier 2, infopass), and two of them said the only thing they can do is submit a e-request for me but because I already had one pending they couldn't. Another two told me they can get someone from my local office to contact me regarding a I-551 stamp. Eventually, I got someone from San Francisco field office to call me and they sent me a paper saying that my I-551 is approved, and I will be receiving it via mail in the next week or two. I still don't know why I can't get my 48-months extension. I was also told that my second e-request was already assigned to an officer, but it's been 3 weeks now and I kinda doubt that officer will respond in the next week before the request expires again.
Anyway, you can tell I'm full of frustration