Please post a single statement by any responsible UN official stating that the UN accepts the Indian position/interpretation of Simla.
Here is 'proof of rejection' from their official website:
In July 1972, India and Pakistan signed an agreement defining a Line of Control in Kashmir which, with minor deviations, followed the same course as the ceasefire line established by the Karachi Agreement in 1949. India took the position that the mandate of UNMOGIP had lapsed, since it related specifically to the ceasefire line under the Karachi Agreement. Pakistan, however, did not accept this position.
Given the disagreement between the two parties over UNMOGIP's mandate and functions, the Secretary-General's position has been that UNMOGIP could be terminated only by a decision of the Security Council....
https://unmogip.unmissions.org/background
The UN's reluctance to mediate has nothing to do with the Simla Agreement. The UN made no serious effort to resolve this dispute after the early 1950s. By the late 1950s, the UN was urging Pakistan and India to settle this matter "out of UN" ... Later, the USSR used "the veto" multiple times to avoid discussion on Kashmir in the Security Council. Simla Agreement was signed in 1972 only. So it's not Simla that has made the UN practically irrelevant. The U.N had already been virtually elbowed out of the Kashmir dispute by Russia. However, the Simla Agreement no doubt does give the UN a little bit of "face-saving"...
No UN Sec-Gen, or any responsible official, can say that the UN has no role to play in Kashmir after the signing of Simla agreement, or that the UN Resolutions have become invalid now, or the Simla Agreement supersedes the UN resolutions, as long as Kashmir remains on the agenda of the UN Security Council as an unresolved international dispute, and with the UN observers still present in India and Pakistan to
observe ceasefire violations on the disputed border.