However, he could not enjoy his rights and incoming as a bishop or as a count at all, because the greater part of the lands of his diocese was occupied and unlawfully seized by the oligarch Matthew Csák, who expanded aggressively in Upper Hungary in the first decade of the 14th century. Matthew Csák turned against Charles and even laid siege Buda in June 1311. The monarch sent an army to invade Matthew Csák's domains in September, but it achieved nothing. Since then, constant warfare struck Upper Hungary and the surrounding counties. In the following years, the oligarch's faithful partisan, Simon Kacsics launched massive attacks against the Diocese of Nyitra in order to expand their influence. Around October 1313, he besieged and captured the diocese's seat, Nyitra Castle on behalf of Csák, causing serious damage in the walls. He handed over the fort to his lord and became its castellan thereafter. Subsequently, Simon plundered and looted the surrounding episcopal estates and villages. Years later, John recalled that after the seizure of Nyitra Castle and destroying several episcopal villages, Simon loudly abused and intended to stab the bishop with a sword in the presence of Matthew Csák, but the powerful oligarch prevented him by his admonition. Thereafter, Simon blasphemed John with disparaging and blasphemous words. The cathedral and the associated buildings (chapter seat, library, towers etc.) were completely looted and burnt by the Csák troops. The relics of St. Zorard and St. Benedict were also destroyed, in addition to crosses, chasubles, calyces and bells. According to estimations, the cathedral suffered altogether 2,000 marks of damage as a result of continuous plundering raids.
