I'd just assign it to the person who made the change and tell them to deal with it.Fucking work - again.
Someone makes changes at 8:30am this morning. Customer then calls up to say everything stopped working at 8:30am this morning,
Call gets assigned to me instead of person who made the changes. Person who made the changes then claims this is completely unrelated and therefore isn't going to help as its nothing to do with them. 3 hours of pissing about trying to work out what has happened as nothing has been documented and surprisingly enough it was the change made this morning.
This happens on a regular basis.
Surely the first thing to try is reverse what they did? If they didn't document what they did, it's their problem.