Contradiction with Amos 3:7
This verse states that God reveals His plans to prophets, contradicting Isaiah 20 where God acts through Isaiah without a prior revelation of the purpose.
Amos 3:7: Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets.
Contradiction with Jeremiah 29:11
This verse assures a future and a hope, whereas Isaiah 20 depicts a sign of impending doom carried by Assyria.
Jeremiah 29:11: For I know the thoughts that I think toward you, saith the LORD, thoughts of peace, and not of evil, to give you an expected end. [expected...: Heb. end and expectation]
Contradiction with Hebrews 13:8
Suggests God's nature is unchanging, while Isaiah 20:1 shows God using Assyria as an agent of change and judgment.
Hebrews 13:8: Jesus Christ the same yesterday, and to day, and for ever.