It does sound like a stripped thread. put some mole grips on it & pull hard while turning it. With any luck it will be the handle itself that will be stripped. You can buy them at any caravan shop. If the clamp thread is stripped then that will have to be unbolted from chassis & replaced. Ensure you get correct size clamp if it needs changing, caravans are usually 48mm jockey wheel shaft diameter. Handle threads are all the same afaik.
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