Exploiting a loophole to the consumers pocket

We had a bond with Standard Bank since 2010 for vacant land that we bought. The bond was paid of in 2017 plus an additional amount that we paid in by mistake. We wanted to cancel the bond now, so that the amount in credit can be paid back into our account only to find out that Standard Bank activated insurance on the bond(that is in credit) somewhere in 2018. This bond for vacant land, as it was specified on their system, was paid off in 2017 with no insurance but now that we are in credit there is insurance to the amount of R 3 487 and that was activated months later in 2018. On querying Standard Bank, that did not want to give us a loan when we wanted to build the property I must add, their representative said the insurance is because there is now a house on the stand, which they activated the insurance for. We did not ask for this to be done as we have our own insurance through Santam. Also as far as I'm concerned the house can not automatically be regarded as any of their business as their loan agreement clearly states that it is for vacant land. How can Standard Bank be allowed to charge any insurance on a zero bond for a property that they had nothing to do with and that without my permission? If this is not taking advantage, I don't know what is, and that for R 3 487. For an institution or their size that's a tee and cake bill. For a consumer that's a lot of money. Shame on you Standard Bank.