var lat = 50.5524; //Coordinates of Wetzlar, Germany
var lon = 8.5072;
var zoom = 12;
var tileLong = long2tile (lon, zoom + 1); //For some reason I need to increase the zoom level by 1 to get equivalent results in WMTS and OSM
var tileLat = lat2tile(lat, zoom +1);

tileLong -> 4289, this is correct as the OSM and the WMTS tile have the same value
tileLat -> 2758, correct in OSM, incorrect for WMTS as WMTS needs inversing the y-axis

var invertedTileLat = (1 << zoom) - tileLat - 1; //I have also tried zoom+1

invertedTileLat -> 1337, still incorrect for WMTS. The expected result is 897