case number is on the back of your check

so, look at the back of the cancelled check, you should be able to find the case number, mine is from Texas center, so it starts as "SRCXXXXXXXX"
then, go to USCIS website check your status... link as follow:
https://egov.uscis.gov/cris/caseStatusSearchDisplay.do;jsessionid=acbNFD66V6Lsq6E_n0Pvr

BTW, thanks.... it's truely a big relief! Good luck!