Board Thread:News and Events/@comment-26176272-20150306192838/@comment-26005122-20171012225127

You're going to have fill out an inquiry form to the developer in the Tsum Tsum app. In the Options menu, go to Help - Inquiries - Inquiries - scroll down to Inquiries - I Agree (Proceed to inquiry form). And fill out the form they have there about your lost purchase.

Although, it is possible you may have just gotten a duplicate Tsum, and not realize it. If you have a large collection already, it may be impossible to tell.