I'm having the same issue, trying to move my itunes account to a new country is being a huge pain. The only way you can cancel your subscription to Itunes Match is by contacting Apple support. Having said this, Apple support emailed last night stating that it is not currently possible to cancel my subsription to iTunes Match! And they have no estimated time on resolving this issue.
I suggest, if you haven't already done so, that you check out the conditions and limitations of moving your itunes account to a new country, plenty of information on this topic in the forums.
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