You would have lost the $11.20 had you cancelled.

The points normally credit back to the account straight away, but there can be a delay sometimes.

With it not being 100% guaranteed that the points would have returned to your account on the call, I would say you did the right thing in your circumstances. Had you been willing to take the small risk that you may have to wait a number of hours for the points to return, then cancelling would have been the better option to save $88.80.

Very much a case of whatever works best for an individual. If you got your revised flights reserved for the new dates, I'd chalk it up as a successful result none the less.