I suppose it depends whether it was before or after check in - once checked in, I doubt it can be changed for those flights you have checked in for. And not sure about points being transferred either given one is Avios and the other Velocity, but also, status credits cannot be transferred at all.
Having had the QR Platinum experience (and I still am as they keep extending it!), I decided while their in-air experience is fantastic, their aftersales and phone is soooo bad that I doubt I'll fly them again, simply because when things go wrong they just do not care, despite what they say they will do, in my experience nothing ever happened. And this was a number of issues over different flights. So with that in mind, I would be concerned about what you are being told as I think it unlikely to happen