To cryptographically verify that both donations were indeed made by me, have a look at the input addresses of both transactions and use any of the available tools (most desktop Bitcoin wallets) to verify that below messages were sign with the addresses' respective private keys.
Address:
15Xt1kTpk5iTCoG1Amze1EFPpr6Cnn3JbH
Message:
mariodian.com owns the above address that was used to donate 0.0099 BTC to 3DNB7HEtawnvRbkhqJ34WNLBhoiwMSCUY3 owned by freeross.org
Signature:
IHhv18o7Ie7jqTN1UgCO82A+arQxVEB4AU4BlWB4EmBQZc059Y8JrIt+4a40QCX5zPQgblDf5+7MgDciOXnPCrQ=
Address:
11588oAxDfYzFnC78wDqyrTyimjUfefL9E
Message:
mariodian.com owns the above address that was used to donate 0.02475 BTC to 3DNB7HEtawnvRbkhqJ34WNLBhoiwMSCUY3 owned by freeross.org
Signature:
H1jDvEUl4H05XEwkt/6DvbgbS1BFuJ2i+SGAf5+OPQAgShob4uztRl6h4+MeV9gvPMd+3E/Srn0FSNnWFavaerU=