Found those posts in another forum with similar number +38681897034 also from Slovenia.
"Got a call from thus number this evening, called it back and i get the recording of the audio track from some type of pornography"
"Got the same seedy call..I'm on Vodafone too..rang the number back and got the same porn style recording.."
Seems to be a porn line and if you ring back probably they will charge you...