Got to stage 21 in Tower Defense Game Event and no reward

So basically I was just playing the "Tower Defense Game Event" with my friend and it took many tries until we could find a good party with a good party we got to stage 21 everyone except me got the achievement and the reward Swift Zhevra mount at first I thought okay maybe I don't have enough space in my inventory so it got sent the mail I checked the mail to find nothing there then I double checked my inventory and I saw I had 1 slot left so it couldn't go to a mailbox so I was wondering is there a chance I could get it as its sees like some kind of error I have a few screenshots of me playing there reaching stage 20

https://imgur.com/a/mUKJkg
Links so u can truly see i was there y user is Slapiashduo a friend of mine did the screenshots btw he's a rogue
https://imgur.com/a/ZmwHH3m