I entered the university for the 2nd year of bachelor's degree on the basis of a diploma...

... junior specialist. The university requires payment of the academic difference for 1 year, which actually makes up the full cost of studying in the specialty per year. At the same time, I was not given a detailed calculation for what, how much to pay, but only the amount and the account number. I was interested, in other universities it is allowed to take the missing subjects during the year together with the current first year. Is it legitimate? What laws and documents regulate this? There is no such information on the university's website, nor in the study contract. I can't get through to the MES hotline.