Something else I noticed about your ad. The part at the end where you mention you could end the listing early due to being advertised elsewhere, another big no no. Another breach of policy. You can't advertise something on eBay and also elsewhere. I'd advise revising your listing and removing that sentence.

In regards to the posted question in the ad, the bidder can cancel his own bid, or you can do it for him. You don't need to contact eBay for that. 

For your buyer to cancel their own bid, they need to click on this link http://offer.ebay.com.au/ws/eBayISAPI.dll?RetractBidShow

For you to cancel a bid, you can do that here, http://offer.ebay.com.au/ws/eBayISAPI.dll?CancelBidShow