Often used in horror movies, when the female victim answers the phone, jumping straight into conversation assuming it's their girlfriend, and it ends up being the killer.
If we go by TV tropes, this trope would be a variant of the Evil Phone trope. I would call it The Reverse Evil Phone. In the Evil Phone trope the character thinks it's the killer calling, but it ends up being someone else, which then guarantees the next call will be from the killer but the character think it's the first caller calling back. The scenario you describe would therefore be a Reverse Evil Phone trope.