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Sure - I've just explained to them the reasons why the cheques weren't cashed at the time and requested a re-issue. I've said that I was told on the phone that the cheques were no longer valid but that I would have to pay a cancellation fee, then I've asked why they need to be cancelled if they aren't valid. I've enclosed my cheque for the fee and asked if they could please explain exactly what that charge is for, or return my cheque if it no longer applies. Kept it all polite and business-like! Have sent it off recorded delivery but no reply yet!
I found out that there are some 'reclaim services' people who offer to do all this for you, but they also charge and it's more than going stright back to the issuer itself, so I avoided those. Good luck with yours - you might find it useful to sign up to www.moneysavingexpert.com which is a really good website for all things money-related, and you could also ask there what people have done about reclaiming charges. Sometimes there are model letters posted there as examples.
Hope you are successful!