Ten instances on Universal Channel (Slovenia) were reported to the regulator, which licenses the channels from the UK. It was found that Universal had exceeded the 12 minute allowance under the Code on the Scheduling of Television Advertising by up to five minutes.
There were eight instances on Discovery Channel Slovenia between November 30 and December 20 where the limit had been exceeded by 28 and 56 seconds respectively, totalling 260 seconds.
Both channels use a cue tone system to insert local advertising.
Universal said the system was not able to handle locally inserted advertising where ad breaks had been moved to an adjacent hour. It has reviewed its procedures.
Discovery said its problems were down to overbooking and offered to reduce its advertising for a short period to compensate.
Ofcom intends to continue to monitor both broadcasters.