Albert Barnes on 2 Corinthians 10:11

Let such an one think this, etc. Let them not flatter themselves that there will be any discrepancy between my words and my deeds. Let them feel that all which has been threatened will be certainly executed, unless there is repentance. Paul here designedly contradicts the charge which was made against him; and means to say that all that he had threatened in his letters would be certainly executed, unless there was reform. I think that the evidence here is clear that Paul does not intend to admit what they said about his bodily presence to be true; and most probably all that has been recorded about his deformity is mere fable.