If you mailed the signature with the letter requesting it to the address on the letter, and included a copy of the letter of case number then it should be processed.     It might be on hold though.

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**NOTE*** Due to the Corona virus the IRS is operating short staffed. All field offices are closed and some processing centers are all but closed. Any tax return that requires hand processing will probably have long delays. Mailed returns are not being processed at all at this time. Most phone service has been curtailed.
https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue
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Thank you. Since I haven't heard anything, do I really just sit around and wait then? It seems like any time i try to connect directly with the IRS to check, I can't get through to them or get anywhere. And when I use the "check status of refund" -- it says "can't find the status, when did you file"... so I put in "January 20th (when I first filed, and then the IRS reached out mid Feb with the signature page request)... and then it says "We cannot provide any information about your refund. "

Not sure what else to do or if I just keep waiting on details? It's a large refund so it would be awesome to get it. Thanks so much! 

There is not much you can do other than calling the IRS when they re-open.

https://www.irs.gov/help/telephone-assistance