FYI, if you're not in the top6 arena, you cannot be farmed repeatedly.

Furthermore there's nothing of value in arena stakes unless it's gems or a leadercard. When he takes gemstakes from you, have you asked for them back? Does he power down to give them back? If he's not withholding gems from you, then *offers full cup with a lid*

Otherwise your solutions are simple:
1-- get out of the top6 arena
2-- jump to one of the other realms where you can be in the top6 and not get farmed in arena