Hi Hanna, sometimes sl servers and the merchant boxes don't cooperate too well. As you were advised contact the sellers who will then able to redeliver everything for you. One thought I would like to add though. Make sure that when you are in second life, logged in, you are not AFK or in BUSY mode. In those cases the system automatically declines the incoming products.
Your viewer goes to AFK (IDLE) state after a few minutes by default. You can turn that off in Preferences.