Double premium twice for what ?

My decoder broke and I bought a new one. Contacted the call centre in March to deactivate the broken one. They assured me it was done but they never did. I paid two premiums end of March and I phoned them and they told me they deactivated the broken one and I will have a credit in April. Well April has come and I again got charged two premiums and the decoder has still not been deactivated. Called the customer call line spoke to a lovely lady who would help me but got cut off. What on earth do I do now ?