I agree that you were not properly notified (i.e., served with the lawsuit in the manner required by Michigan law), then you may have grounds to eliminate (vacate) the judegment in Michigan. if you are not able to do so, Florida law has certain protections against their collections efforts. You may also consider bankruptcy, depending on where you ultimately establish residency.
Were you initially notified of the lawsuit and judgment that was lodged against you? If so, then they likely don't need to notify you before seeking garnishment. However, if you weren't served with the summons and complaint in the underlying lawsuit and had no knowledge of it, you need to hire an attorney in the jurisdiction where the lawsuit was filed
This is general advice based on limited interaction in an online forum. The reply does NOT create an attorney-client relationship. You are strongly advised to seek the advice of an attorney in your jurisdiction after you have presented them with all of the facts.