Barclays overdraft repayment

Hi,
Recently stopped our dmp with sc and just trying to self manage everything. Some awaiting CCA response. Two enforceable so we’re paying directly.
We have two Barclays overdrafts. One with only approx £34 left and the other £1800. I tried to call Barclays a few weeks ago. The customer service passed me to collections as it’s a closed account, collections didn't have enough info to verify me via the security checks so passed me back to customer services who tried to find my account via postcode, account number-I gave what I think is the account number but they didn’t recognise it and needed the sort code with it. I don’t have the full details as I cut the card up years ago and all our statements were online at the time. (Will have a good search in the loft for paperwork) but as it stands they can’t take payment over the phone or give me account details to transfer too.
I’ve written this in a letter to them stating my intention to pay both accounts in full but not heard anything back. I’m a bit worried about not paying anything but what can I do if they can’t speak to me or give me a way to pay.
Is there anything else I can do at this stage? (Other than keep looking for an old letter with account details on- even then I’d have to write again because collections don’t have full security info and CS don’t have the account on file because it’s technically closed!)

UPDATE: I found old account info in the loft which was enough for them to find the accounts, just before I called upI had a letter saying my account was in credit!! £77 coming via cheque woo hoo! Hopefully when hubby calls his balance will be less too and we can finally get these paid off!