UPDATE
Optus agreed on Monday to let SBS broadcast a handful of matches that were intended to be exclusive to the telco, essentially buying itself 48 hours to resolve all issues.
That run of content will end on Wednesday morning (AEST), after Russia tackles Egypt.
"There's no doubt this has adversely affected the Optus brand ... everybody is very disappointed, to put it mildly," an apologetic Lew told reporters on Monday night.
"We will use the two days we have ... to robustly test the systems under different loads.
"We believe by that time we will have the technical issues resolved."
EARLIER
Prime Minister Malcolm Turnbull has spoken to Optus boss Allen Lew amid outrage among football fans at repeated disruptions to the telco's World Cup coverage.
Mr Lew was forced to apologise to fans on Sunday after broadband streaming issues marred the telco's coverage of the World Cup's opening games.
"I apologise unreservedly to all Australians," Mr Lew tweeted.
"We should have done better, we can do better and we will do better."
Many fans took to social media at the weekend and on Monday, blasting Optus for the problems marring its subscription streaming service.
Mr Turnbull stepped into the debate on Monday, seeking assurance from Mr Lew.
He told parliament Mr Lew acknowledged there were problems.
"He believes he can fix it and it will be fixed tonight and obviously those other bands will be expecting Optus to deliver in that regard," the prime minister said.
Optus has blamed the dropouts in its service on "an extremely high number of viewers logging into our platforms just before kick-off causing some systems to overload".
Feed disruptions plagued the telco's coverage of its first exclusive match - Uruguay against Egypt - on Friday night.
Irate viewers took to Twitter to vent their frustrations, coining the #FloptusSport hashtag.
Some fans who watched the Socceroos take on France on Saturday night using the Optus Sport app also had buffering issues.
And on Sunday night, more fans complained about coverage disruptions on the Optus Sport app during the Costa Rica and Serbia match.
"The world cup coverages is very poor quality, so many times happens that i had to refresh the page, after i did that unfortunately coverage could only lasted for about few seconds," one Optus subscriber known as Gooners74 wrote on Optus Sport's online forum.
"We are very upset, this is once in 4 years even, as a customer or customers in general we deserves better!!!!!!"
Another subscriber, Skilla13, complained of similar issues during Sunday night's clash between Germany and Mexico.
"This is a disgrace by Optus. Should give everyone their money back," they wrote.
The Australian broadcasting rights to the tournament are being shared by Optus Sport and free-to-air network SBS.
But SBS only has the rights to one match a night and every match from the quarter-final stage onwards, as well as each Socceroos contest.
Optus will be the only provider to stream every game of World Cup catching out many football fans used to seeing all the games on SBS.
Paul Fletcher, parliamentary secretary to the communications minister, rejected Labor's claim that budget cuts to SBS forced the broadcaster to licence World Cup games to Optus.
He said SBS management made the decision to share the World Cup rights in exchange for some English Premier League games.
Australian Associated Press