Your situation is not uncommon or unique. Here's another instance.
Problem is you have at least two parties involved. The culprit is the local ATM owner (the Guatemalan bank), which has already charged Wells Fargo for your withdrawal (and Wells Fargo has debited your account). See, you're not out $266, you're out 2,000 Quetzals.
If the Guatemalan bank doesn't own up to the mistake to WF, WF would have to take the loss on your withdrawal.
You need to get pissy with the Guatemalan Bank. They cannot simply tell you to go to the US bank. It's their ATM they have your 2,000 Quetzals.
You are likely to run into a brick wall. So, put it all in writing. Keep copies of everything. If the Guatemalan bank doesn't give you the 2,000 Qs, THEN take it back to Wells Fargo.
If that doesn't work, then file a complaint with BBB (against Wells Fargo). (free online...you can do from Guatemala.). If THAT doesn't work, take it to the media when you get stateside.
Be a nuisance.
Unless the Guatemalan Bank is part of Wells' "preferred" international correspondents, there is no real incentive for them to make you whole. And the only incentive for Wells to take the loss, is retaining you as a client (your future business may not be worth $266 to them).
I'd give you better than even odds of getting your money back, if you insist on it.