@James ********
I haven’t heard of it happening either. But I’ve been either visiting or living in Thailand since 1978, & one thing I’ve learned is that nothing should surprise you regarding anything related to Thailand. Hence the saying, TiT.
As to whether or not Bangkok Bank would close the OP’s account if he refused to renew his insurance, consider (1) the refusal itself would likely be taken as a loss of face, & (2) most Thai with any authority often flex the boundaries of that authority with impunity. In one example, an immigration officer once changed my extension from “married” to “retirement” because he didn’t want to deal with organizing the documents & sending them to Bangkok for approval. At the time, I was considering eventually going for permanent residence as a prelude to applying for Thai citizenship, neither of which I could accomplish on a “retirement” extension. When I tried to make a case, he raised his voice & said, “is there a problem?” Having just learned of a fellow farang being denied his annual extension after seven years of living in Thailand, I curtly responded, “no sir” & left before he could change his mind about my renewed-but-changed visa extension.