You can request a cancellation but the seller does not have to accept.
However, under eBay's 30 day MBG Money Back Guarantee policy, this is written on every listing on the right hand side, if you do not receive your item within a reasonable time, you open a case for item not received and will receive a full refund if you claim within 30 days f the item's last estimated date for delivery.
Wait no longer but proceed this way now:
Go right of the item purchased, and from More Actions select.... I Have Not Received My Item.
If you are not fully refunded within 3 days, you must escalate the case on day 4 or within 30 days from opening the case, and eBay will step in and force the refund.
Do not close the case early for any excuse or promise the seller may give, and do not forget to escalate.
@abujjux