My mother is 85 years old, she does not receive a pension supplement of UAH 500

Perhaps this is due to the fact that your mother's pension, together with compensatory payments and allowances, increases, in particular, a pension for special services to Ukraine after carrying out the calculation, exceeds UAH 9,205.19 (in accordance with the Resolution of the CMU dated 01.04.2020 No. 251 ).

If this is not the case, then submit an electronic application on the website of the Pension Fund of Ukraine (https://www.pfu.gov.ua/23131-elektronne-zvernennya-aplikatsijna-forma/) or contact the branch of the PFU at your mother's place of residence.