If you use /gift and it fails, you do not have any gifts in your inbox. If you do have anything, /gift will open a gui menu that tells you who sent you the gift, what items are included, and how many of those items there are.
Either:
1) You have the heads in /gift but didn't know how to claim them. I think items expire if unclaimed for 7 days, so make sure to check.
2) The person sent the heads to the wrong person by tabfailing (someone else has your items, you still lost 20m)
3) The person straight up scammed you (you lost 20m).
Good luck!