Counter Offer/Promotion in writing reneged on

Recently I was offered in writing a promotion to a higher sales management position with another company. My current company scrambled hard to counter offer. They put together an effective counter offer, including a promotion on a certain date provided I hit certain numbers. I would not accept the counter & agree to stay until certain questions I emailed detailing our agreement of the counter offer terms were answered in writing. I received an email from the VP answering these questions and agreeing to the terms we had discussed. I have saved and printed all emails,texts, etc. detailing the terms and agreement. I hit all of the numbers requested of me. However, some time has passed from the date and there is no movement. If they renege on their counteroffer, do I have a case? Thanks for any help.