Contradiction with Isaiah 46:10
While Isaiah 41:26 suggests no one could declare the events, Isaiah 46:10 states that God declares the end from the beginning.
Isaiah 46:10: Declaring the end from the beginning, and from ancient times [the things] that are not [yet] done, saying, My counsel shall stand, and I will do all my pleasure:
Contradiction with Acts 15:18
Isaiah 41:26 implies no one declared the events from the beginning, but Acts 15:18 mentions that God's works are known from the beginning of the world.
Acts 15:18: Known unto God are all his works from the beginning of the world.
Contradiction with John 16:13
This indicates that the Spirit of Truth will guide and declare what is to come, which contradicts the notion that no one could declare it, as in Isaiah 41:26.
John 16:13: Howbeit when he, the Spirit of truth, is come, he will guide you into all truth: for he shall not speak of himself; but whatsoever he shall hear, [that] shall he speak: and he will shew you things to come.
Contradiction with Amos 3:7
Amos implies that God reveals His plans to His prophets, which contradicts the notion in Isaiah 41:26 that no one declared the former things.
Amos 3:7: Surely the Lord GOD will do nothing, but he revealeth his secret unto his servants the prophets.
Contradiction with Isaiah 42:9
This verse suggests that new things are declared before they spring forth, contrasting with the claim in Isaiah 41:26 that such declarations were not made.
Isaiah 42:9: Behold, the former things are come to pass, and new things do I declare: before they spring forth I tell you of them.