Greetings @Pandvin! I apologize you're having issues retrieving your items. There are a couple of ways that you can get your mounts from silver to gold.
One option is to have someone who is transferring servers, to bring the items with them. A second option is to log-in to PRO Player Dashboard and transfer your main Silver account, to Gold Server. When doing this there is a clean swap of progress of each server. It is important to know that each player only gets one free transfer per 30 days. You can transfer more than once per month, but each additional transfer does cost a fee of 100 coins.
I hope this gives some clarification. If you continue to run into issues please reach back out. I look forward tonseeing the progress of this topic.
-Hazegeek