Source is these I think ?
https://topwar.ru/164587-kak-bystro-popolnit-tankovyj-park-pakistan-zakupaet-t-55.html
Pakistan buys second-hand goods While India begins production of five hundred T-90MS for $ 4 million each, things are not going so well in Pakistan. Al-Khalid production is proceeding at a slow pace (about a dozen a year), the modernization of the T-80UD is stalled. Therefore, we decided to purchase very modestly so far - the modernized T-55s with NKDZ from Serbia
And this
https://topwar.ru/164587-kak-bystro-popolnit-tankovyj-park-pakistan-zakupaet-t-55.html
Against the background of the deployment in India of the release of a new large-scale batch of the main battle tanks T-90MS, Pakistan is forced to take asymmetric actions, trying to quickly replenish the ranks of its military equipment. The high cost of modern tanks does not allow Islamabad to acquire an impressive MBT fleet of advanced technology. Apparently, precisely because of material difficulties, the production of Al-Khalid's own-designed machine is in miserable quantities. About a dozen units are produced throughout the year. The T-80UD improvement program is slipping.
Under these conditions, Pakistan made a fairly budgetary decision, acquiring an improved T-55. The machines intended for Islamabad received a complex of dynamic protection. As stated in the press, the T-55 data were purchased from Serbia, although it is believed that they are “originally” from Slovenia. In Russia, the last T-55s were withdrawn from service at the turn of the 2010s, although various modifications of this medium tank are offered for export. This machine is very popular among countries with a modest military budget. The financial difficulties in Pakistan most likely led to the decision to purchase the T-55