Sorry, but you cannot change from MFJ to MFS after the filing deadline which is why the amended return was rejected.
And you are allowed to file a joint return no matter who earns what and it is a better filing status all the way around ... did you amend both your returns? Did you not see that you owed more taxes by filing separate returns? And you said "fiance" ... were you not married as of 12/31/16?
