Paying double insurance because they refuse to respond

On 4 January, they send me a policy document for new insurance out of the blue. I can't remember if I signed up for it a year ago or not (when we signed the building loan), but on that same day, I responded to that email and asked them to immediately cancel the insurance and provided proof of my own insurance that I've been paying for two months already.

I've sent multiple emails, I spoke to a home loan consultant on around the 6th about it and they just said to send proof of my insurance to the email address I already sent it to. I contacted the Insurance complaints department and even the main complaints department at Standard Bank. Nothing gets these people's attention. The main complaints department responded a couple of times and helped to force the home loans side to finally respond to queries on their side but they seem powerless to get anything done on the insurance side.

As a desperate measure, I'm considering stopping payment on the home loan altogether until they cancel and refund my insurance premiums. The fact that they're negligent on their side and not reading their emails shouldn't cost me money. I'll first see if anything gets resolved through this complaint before resorting to that.