If you did not see any button that ask to confirm receive, Shopee will auto cancel & refund to you. If that button appears, and shopee guarantee used, then expired, it will still automatically release to seller. Your only choice is to file dispute. Upon seller reject there should be a way to raise dispute somewhere... can't remember the location.

Depends. Longest it takes up to 3 days for me, then another 3~5 days for money credited back to my bank account. I rarely file dispute since most item bought from well aged Seller (at least 6 months beyond) with so so review and/or cikai value item.