The error code is
Cause i = 0x8281 - Unallocated/unassigned number
Meaning:The switch receives the ISDN number in the correct format. However, the number does not belong to destination equipment.
82 code means the problem is at the telco switch. Most likely telco does not have routing for that number. I had several issues where telco's routing was screwed up. Give them a call and ask traffic engineering to look into routing for that number.