What release of SAS are you running?
What do you mean when you say the the MNAR statement is not "activated"? Do you get an ERROR message in your LOG that suggests something went wrong with it?
Provided that you are running SAS/STAT 13.1 or SAS 9.4TS1M1 then you should be able to use the MNAR statement and the FCS statement together in a way similar to this example.
http://support.sas.com/documentation/cdl/en/statug/66859/HTML/default/viewer.htm#statug_mi_examples16.htm
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