As I already pointed out (to which you merely reiterated the same one liner), the UNSG does not share your interpretation of the Simla Agreement, and you have neither established anything in favor of your position nor anything against mine.
In fact, by offering to mediate between India and Pakistan, the UNSG has thrown your (and India's) interpretation of the Simla Agreement into the garbage, since the mediation offer explicitly supports the principle of third party involvement, and would not have been made under ANY circumstances had the UNSG shared your or India's interpretation of the Simla Agreement.
Mine is not an opinion, it is fact, based on the clauses of the Simla Agreement, yet to be countered by you.
Paragraph one, by reiterating the commitment of both States to abide by the UN Charter (and therefore abide by any binding UNSC Resolutions) clearly accepts the principle of third party mediation.
Paragraph 2, by virtue of referencing "other peaceful means mutually agreed upon them", also accepts the principle of third party mediation, since "third part mediation" can fit the definition of "other peaceful means mutually agreed upon between them". In addition, the existing UNSC resolutions on Kashmir, by virtue of having been accepted by both States, constitute the only existing "peaceful means mutually agreed upon between them" and therefore continue to be valid.