Cancelled insurance

On Friday 28/08/2017 we received an email from Nedbank to say that my home insurance was cancelled due to none payment. I checked the policy number just to find out that this was my previous home's policy number which I sold in March 2017. the bond was paid up and according to me, there should not exist any policy for this account. I called 16 times to the call center, and insisted that they sort this out and call me back, just to be told that they are not allowed to call the clients back. I have not missed one payment on my bond or insurance and I insist on a letter from Nedbank to say that they have made a mistake and that I have not been cancelled for none payment. Till this date, I have not received any call from Nedbank to assist me. I am currently standing inside Nedbank Brackenfell, and was told they can not assist me and that this is a call center issue. I find this unacceptable.