Unlocking a SAMSUNG device

We are switching providers - very unhappy with AT&T service.  One of the phones on our current AT&T plan is a SAMSUNG S10E.  We went to the local AT&T store yesterday to have them help us unlock this phone.  They were unable to help us - the "unlock" tool keeps stating this phone is not on the AT&T network - which clearly my bill shows every month it IS!!!  They gave me a number to call to talk to "advanced technical support".  Have tried 3 times to call this number and went through the menu options - even asked to talk to a representative - but it kept me on the automated system and kept sending me back to the online tool for unlocking the phone.  I really need someone to contact me personally from Advanced Tech Support to get this phone unlocked.  Please send me a direct phone number (not the 1-800-288-2020 number that the AT&T store gave me).

This is very indicative of why we are leaving AT&T - they are not customer focused.