In a statement, the UOKiK says it opened proceedings against the operator in January 2015.
Its concerns were raised when UPC went about increasing its prices for internet access by PLN7 a month from December 1, 2014.
In UOKiK’s view, UPC illegally informed consumers of the changes to the monthly charges and the agreement the company had used did not contain the appropriate modification clauses.
As a result, it has called on the operator to reimburse customers for each month they paid the increased charge until June 2016.
It has also told UPC to inform consumers of this fact, and publish the decision in a national daily and on its website.
UPC has decided to appeal the decision in Poland’s Court of Competition and Consumer Protection.
It says the changes it made were in accordance with the regulations in telecom law and common market practice and unquestioned at the time by the UOKiK.