Or sold a blank map card by a rogue
If it's a 16gb or 32gb card it show it as such.
Assuming it was / is a valid mapcard you would have highlighted the files to delete - not reformat.
Take a copy of your existing card and then copy that onto the new mapcard to test. In the car it should recognise your maps you have copied across as mib1 and work. If it doesn't do this it's a corrupt card, return it to them.
If it is seeing your old map files then progress following instructions linked. Suspect you might not get this far.