Result!

With the greatest thanks to Grace, after my first complaint failed, I submitted a second, from a different standpoint. In my initial complaint I suggested that I thought it was perhaps illegal for their customer services people to deliberately mislead me. In my second complaint I suggested that whilst they were no doubt entirely within their legal rights, having had their Terms & Conditions written to ensure that was the case, how would they feel, on a personal level, if their employer had done the same thing to their own grandmother. Would they feel proud to be working for such robust business-people or would they feel sick to their stomach?
That seems to have done the trick :-)