Payment of electricity according to a multi-tariff meter

Hello. I have a direct contract with Mosenergosbyt "Western Networks" concluded in 2006. They assigned an account and issued a book, specialists installed a 3-phase two-tariff meter and sealed it. All these years I paid for electricity at two tariffs T1 and T2. But in 2016, information on debt in the amount of 49,000 came to my mobile phone. I began to find out and it turned out that a single-rate counter was registered in my account and the counter number did not match mine. KO claims that I have to pay extra for all years on single-rate indications. I have all the receipts, but they don’t want to listen and understand. Some kind of lawlessness. What to do to sue them? Tell me!