Contacting Branch for reassignment

Has anyone contacted branch for reassignment after getting promoted and was told" I understand you are not slotted in your current grade however, you will have to stay for 36-48 months, and will not be considered for movement until then." Currently, there are two SFC positions on post and both are currently filled. I am now classified as excess personnel however, branch says I can not be moved due to not meeting  the PCS requirements.