That depends on how you left it with the client.
If you've left when they seem content with the outcome and said, ' if it still not right, give me a ring.'
This leaves the ball in the customer's court. What you don't want to do is keep reminding them of the problem, which, for all you know is now sorted as far as they are concerned and if it is not they will let you know - because that is what has been agreed to.
If on the other hand you've left knowing that the issue wasn't fully resolved, then the ball is in your court to keep on trying to resolve it.
There is no difference in the quality of service provided , you're still attending to the problem and the first way leaves the customer in control of the issue, exactly as it should be and if they don't ring you back, they knew that they could, as that is how you left it with them.
If you told them you would ring them in a few days and didn't , that's naughty.
Simon