Redirection normally means that the phone tried to contact Snom's autoprovision service (which is what STUN phones rely on). Was this set up as STUN even once? Or maybe it belonged to someone else who added it in Snom's provisioning servers? Or there is a DHCP option 66 on your network?
1. Check the above points first
2. Check Firmware, upgrade to the correct version if needed
3. Provision it using the default templates, as per our guide