Mathews had already made his feelings clear in the press conference after the defeat that ended Sri Lanka's hopes of progressing at the World Cup, saying Shakib's appeal for the controversial dismissal had been "disgraceful".
He had breached the World Cup rule that a new batter must be ready to face a delivery within two minutes of a wicket falling.
Mathews said in a post on X, formally known as Twitter, that he had been in place with seconds to spare before the chinstrap on his helmet broke requiring a new one to be brought out, backing up his position with time-stamped video screenshots.
"Video evidence shows I still had five more seconds even after the helmet gave away!" he wrote.
"Can the fourth umpire rectify this please? I mean safety is paramount as I just couldn't face the bowler without a helmet.
"This is clear cheating, I want justice," he added in another post.
That directly contradicted fourth umpire Adrian Holdstock.
"In the incident this afternoon, the batter wasn't ready to receive the ball within those two minutes even before the strap became an issue for him," he said in an on-pitch interview after the game at Arun Jaitley Stadium.
"As a batsman, I think you need to make sure you have all your equipment in place... because you actually have to be ready to receive the ball within two minutes, not ready to prepare or take your guard."
'SPIRIT OF CRICKET'
There was plenty of support for Mathews, with former South Africa bowler Dale Steyn saying the incident "wasn't cool", Australia's Usman Khawaja calling it "ridiculous", and former India captain Gautam Gambhir branding it "pathetic".
"I didn't enjoy what I saw out there," Pakistan great Waqar Younis said in a TV broadcast.
"That wasn't good for the spirit of cricket. I am old school and I think that was a lot of drama to get Angelo Mathews out."
Former India cricketer Mohammad Kaif was among those who blamed Shakib for appealing for the dismissal and not reconsidering even after being asked by the on-field umpires whether he wanted to continue with it.
"Shakib should believe in winning, but not 'winning at all cost'. That was shameful," he posted on X.
Shakib had defended his decision in his post-match press conference, saying his actions were within the rules and he had no regrets.
He was supported by former England captain Michael Vaughan, who said in his experience the much vaunted "spirit of the game" had always been more honoured in the breach.
"Yes, Shakib is going to get loads of people, particularly on social media, saying he broke the spirit of the game, he's a disgrace," he told Cricbuzz.
"He's well within his rights, it's the laws of the game. It's utter nonsense talking about the spirit of the game, the umpire's got it right."