the actuator that releases the latch is toast. you will need to change the latch assembly. make sure you retain your original lock cylinder when you swap the assembly so you can open the trunk with the same key
Go to ebay, search on "2011 Mustang used" (or your year Mustang). Then when you locate a wrecking yard that is selling parts for your year Mustang, send them a message (most will have their site web page posted), and ask them if they have your part.
__________________ It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.