Great, so now we get to spend money on lawyers and time in the courts to decide what information falls under “OK to keep for a good reason”
For data processing purposes like this, you will normally have to rely on the legitimate interests basis. That's the one with the almost entirely non-specific definition, combined with the almost entirely non-specific balancing requirements.
With a case like defending an unjustified chargeback, we might assume that the interest is surely both legitimate and overriding, but even that is only a personal view and not something any regulator has explicitly addressed in guidance, as far as I'm aware. In any case, plenty of other scenarios won't be so black and white.