Hello Meikungkua,
Welcome to the community!
Sorry to hear customer service had advised you to go to the store after your long wait. You should note the forums are community-driven and not intended as a venue for customer services.
That said, are you the owner of both those lines? Since you are intending on separating the lines into two accounts, will you still own both accounts? If someone else is to take responsibility of one of the lines, you would need to transfer responsibility (ToR) of that line to the other person (see here). If that is the case, they will likely require a verification of credit before they can assume responsibility for that line. Depending on the circumstances, they might require it to be done in-store so they may verifiy the new owner's identification.
You should also note that there is a charge for the transfer of responsibility (see here).
Hope this helps 😀
Cheers
