4 Digit Passcode changed to Alphanumeric Password PLEASE HELP

Ok so I've always used a 4 digit passcode for my Iphone and have never changed it from that, but recently when i did my face ID i would see the alphanumeric menu pop up for a second and then it would open my phone but I never used to see this so I angled the phone away from me to see what was going on and to my surprise it was showing a alphanumeric password menu instead of my 4 digit passcode menu, so I tried to put in my 4 digit passcode in it but it didnt work and then I tried a few more passwords that it might of been somehow but it didnt work and got locked out of 1 minute but when it came back I couldnt use face Id so I was stuck out of my phone. I really need help with this, Im going to Mexico in 4 days and need my phone to work, Please help!