I have never used this before so I apologise in advance if this is not the appropriate place to give suggestions to AGL.
It seems that AGL does not have a place in which you can give your preferred name. I understand that the legal name would be required by AGL in order to prove identity and for other legal reasons, but it can be very distressing receiving a bill under a name that you do not use/ that is incorrect. I wanted to recommend adding a section where a preferred name can be added, which should then be used for future bills (with the account still obviously being held under legal name). This would reduce a lot of stress, especially for those who cannot yet afford to have their name changed legally. If fraud or whatnot is an issue, then AGL could simply request a letter written by a mental health professional or GP to support the request.