Neither buyer nor seller can cancel an order forcefully from their side, only support can do that.
If the buyer doesn’t accept but also doesn’t decline the request, i.e., does nothing, the order will automatically be canceled 48 hours (I think, not sure though, consult Seller Help Center for correct time) after you sent him your cancellation request.
If the buyer declined the request, you can request again, or ask support if you don’t think there’s a chance to settle it with the buyer (you did already).
If you both send a cancellation request to your buyer yourself and ask support to cancel for you, you kind of prevent them to do what you want, cancel the order, because they probably are bound to wait out the time your cancellation request granted your buyer for a reply.
However, what do do now… What I’d do is politely ask again if they could cancel the order (repeat reason/s, in a concise and precise form) - important: use the same ticket you opened for the issue (you can add to it), don’t create a new one.