Cancelling a policy

I am trying to cancel two retirement annuities and have sent through a letter with an electronic signature to request this action to be completed. I have received 2 responses via email stating 'the signature is not the same as on their records' I have requested on 3 occasions for them to send me a direct line so I can speak t someone as I am abroad and cannot dial through on the 0860 number at the bottom of the email. As yet this has not been forthcoming and I fear the debit order will still be taken from my account.