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You certainly have redress with regard to the fact that they have damaged the trellis on your side of the boundary - you are entitled to compensation from them (the cost of putting the damage right) - you should either speak with them face to face or send a letter advising them formally of the damage and how much it will cost to put right - you can take them to the small claims court - but hopefully common sense from them will prevail. They are allowed to have the trampoline there I am afraid as long as it is not on your property - even where higher than the fence.
Happy to discuss
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