I would like to make a refund but I don’t know where to get started

i sent my mother $300 on Apple Pay and it went missing and never went through. I sent the money out of my personal bank account and transferred it into Apple Pay so that I can send it to my mom. But when I went to send the funds it didn’t work at first and said that the services were down. I then checked Apple Pay to see what the problem was and there was no money in my account and there was no receipt I believe that the money got glitched out somehow. I tried waiting but I’m down $300 now and I want to get it back as fast as possible. Please can I get some help with this.