It depends on what you want out of the situation. If you genuinely just want to be rid of the client, then just walk away. You've done more than enough already

It depends on what you want out of the situation. If you genuinely just want to be rid of the client, then just walk away. You've done more than enough already. If you want to see if you can turn this problem-client into a good one, then maybe you can talk with them (firmly) about setting up a payment plan or some-other-way for them to pay off the extra work you've been doing. If you want a good reference from the client in the future (semi-important if you're still building-out your portfolio) then maaaaaaybe I'd transition away over 2 weeks or so. But that's only if their reputation is fantastic and they'd make a great reference in the future.