Take control of the call from the outset.
Tell them. "OK Mr Jones, can you tell me very briefly what happened without going into too much detail and I will summarise what you have said'. Empathise with their plight but do not apologise unnecessarily and certainly not for your oown efforts. It is not a chance a pity party but the chance to come to an outcome that they will appreciate.
Do not suggest anything outside of what the company can offer.
Most of the phone companies have call centres offshore and the banks, insurance companies and even the energy companies are following suit. I dunno what kind of companies you work for but I will give you an exampe of a telelphone company type phone call.
Wrong way
"Hello this is bucephalus speaking'
"Finally got through to someone. I have been waiting forever..."
"I am so sorry Sir. Our lines are really busy at the moment and you are right the call cue is really long. We are really trying to answer the calls as quickly as possible. There are just a lot of people calling in"
"I am not bloody surprised. You guys don't deal with us right the first time. I have had three people hang up on me and it is costing me a fortune. What are you guys doing in there?"
"Sorry, you are right. I am sorry they have hung up on you. Do you have their names , perhaps i could put through a complaint about how you have been dealt with?"
"Bad enough that I get the wrong bloody phone and the wrong plan and can't activate my sim card when I try to get through to your stupid company but when i do you hang up on me! Its bloody unbelievable"
"I do apologise i don't hang up on people "
'Everyone else does there. Seems noone can help me"
"I would really like to" (Sees Manger giving you a wind up the call) *Panics because you are no nearer to knowing where you are*
"Umm...Sir could i start by having your name?"
Better way
"Hello this is bucephalus speaking'
"Finally got through to someone. I have been waiting forever..."
"Ok My apologies. To help look after you I am going to have to grab a couple of quick details for verification. Could I have your name and address and your date of birth"
'Oh here we go again...Jim jones..1 Lakeside street, penrith....20/07/1983'
"Thanks for that Jim. Bear with me a moment as I quickly get your account up. Now having a look here i can see notes here stating you have ordered an Iphone 3 on a cap 29 plan. is that correct?"
No...bloody hell. I order an Iphone 4 on a Cap 69 plan! Can't you clowns do any bloody thing right? Is this the best i can expect. Cap 29!..."
"OK Jim i am going to have to just clarify. You were saying when you ordered the phone at the Penrith Branch of Crappy Phones are Us, you ordered an Iphone 4 on a 69 plan but were instead given an Iphone 3 on a Cap 29 plan instead?"
"Yeah."
OK bear with me a moment longer, I have the application you filled in here on the system and i will have a quick look at it there.....You are right mr Jones. You have been given the incorrect phone and placed on the incorrect plan and this is different to what you asked for.
*Manager gives you hurry up sign but you are almost done*
'What I am going to do to fix this situation is...'
That is what I would do were i you mate