@David Zheng No I don't think that you can sue. However, I would like to piggy back off of @Allen Fletcher ...If this happens again, not only would I call the lender daily ... I would get the name of one person and call that same person over and over again. I would create a pain point for that one person ...I'd call every day, then twice a day, next every hour. I would even call every half an hour if need be and ask the same questions over and over (Is it done yet? and Did you get that?). I have even called from a different number when they start sending my calls to voicemail. And Yes, I always leave a voice message. Every. Single. Time.
You will be surprised how well this works and how that "one person" will even check on things outside of their duties. Just to get your file closed and rid of you.
If it's the larger call center situation and I can't get back to the "one person". I write down the names of everyone that I speak with along with the date and time. So if something is not done I have the name of who I spoke along with date and time. This is much more powerful than saying I spoke with "someone" about this already. And yes, I think you should file with Better Business Bureau (BBB) and Federal Trade Commission (FTC) and post on social media site. Good luck to you.