Sunday Times has lost my trust

I made the mistake of taking out a new subscription to the Sunday Times while the old one was still running. The subscriptions dept refuses to honour the second subscription - or indeed provide me with invoices showing start and end dates for each subscription. Thus I have paid twice for the same newspaper. Any telephonic or email enquiries fall into a black hole and nobody resolves the situation or gets back to me. I have been trying to sort this out since April 2018 without success. Please provide me with the service I paid for 15 months ago.