Daniel is correct, that's what I was getting at... but you'd need to go as far as court to get that result.
I've bashed up a quick letter.. see what other people think and see if it can be polished before it's sent.
Dear Navin Ramiah,
On the xxx of xxxx I arranged through the Parcel Monkey website for you to collect and deliver an item for me. I paid for insurance and instructed you exactly what the items were. You agreed this contract, accepted payment and proceeded to lose the item with very little delay.
I'm not quite sure how easy it is to lose an item the size of this package, so I am not yet convinced that every effort has been taken to find the lost item.
On contacting your customer services department by email you've informed me that you cannot be held responsible for your negligence in this case, as you have written in to your terms and conditions that you won't be held responsible for monitors.
I don't believe it matters what is inside the box when it is lost due to your negligence, and having paid for the insurance I now expect you to reimburse me.
Were you to refuse the insurance I would certainly not have sent the item, as a result of you accepting the contract for delivering what was clearly stated to be a Dell Monitor, and your subsequent loss/lack of effort to recover the item I am considerably out of pocket. It would make things simpler for both Parcel Monkey and myself if you were to refund me at this stage, before I take further legal advice. My understanding at this point is that a judge will rule in my favour, and that your terms and conditions cannot be used to escape negligence.
I would greatly appreciate if your reply could reach me within one week of the date of the letter, as otherwise I will assume you wish me to pursue this through a solicitor.
Yours sincerely,
Crater Loads.