*** Moved by Staff to a more appropriate forum. ***Hi guys, I'm new here

I mainly collect postcards but I am also a small-time hobbyist collector of stamps. I exclusively collect MNH Seychelles stamps so as soon as a new stamp comes out, I head on over to the local post office to buy a few stamp sheets. I also purchase older issues online from overseas collectors as many are no longer available locally.
To honor World Oceans Day (June 8th) this year, the Seychelles Post issued a limited reprint from their 1977 'Marine Life' collection, one of which was the 'Zil Eloigne Giant Tiger Cowrie'.

I sent them a message online to purchase 5 sheets. The lady at the post office told me that they had only 1 cowrie stampsheet left. I purchased it and went on my merry way.
Last week I received a message from the post office - apparently they "oversold" the cowrie stamp and forgot to keep a few for archiving. They want to participate in an international stamp competition and have asked me for 3 cowrie stamps, and 3 of the 2019 The 150th Anniversary of the Birth of Mahatma Gandhi limited-print stamps.
Here's the issue: I only have that 1 cowrie stamp sheet and I would have to break that sheet to give them the 3 stamps they need. I'm very conflicted, there's a part of me that wants to help them out but there's another part of me that believes it's not fair for them to put this issue on me. The fact that the post office no longer has stock of it makes it even more valuable.
I am willing to compromise, by donating the 3 Mahatma Gandhi stamps to them, but I am still leaning towards not breaking the stamp sheet. Am I being reasonable?
Any advice would be greatly appreciated, thank you.