IMPOSSIBLE TO GET HOLD OF CANCELLATION/RETENTION DEPARTMENT

I have tried numerous times to get hold of the Retention Department each time getting through to the call centre whether calling 140 ; 143 or 145. Then I have to answer the security questions before they can put me through, once done they say they're putting me through only for my call to be dropped and I never get through. I want to cancel my cell c contract. My last month is end of October and I want to end this contract. I dont want a better deal because you cannot give me one. I dont want a different contract and I dont want to upgrade. I want to cancel. You are quick to help and be there for your customers when they want more contracts and more services but the minute we want to cancel its impossible to get through and have someone help. If someone does not contact me by the end of today I will go to my bank and put a stop to the debit order and I will not pay my final installment. This is ridiculous!!!!