Your eventim.sk order (no matter whether via phone / Internet) is binding.
It may only be cancelled under the conditions specified in the restricted legal terms and conditions (ABGB, KSchG), for example if you have been mislead in the course of placing your order or if the order was placed under duress.
Please note: There is no right of withdrawal for tickets according to § 18 (1) Z10 FAGG.
If you took out ticket insurance when you made your booking, you will find all the relevant information here.