The number of people to complain to media watchdog Ofcom they were unable to vote by phone for Rhydian Roberts in The X Factor has risen above 1,500.
Rhydian was clear favourite ahead of the final
The 24-year-old Welsh favourite was beaten to the title in Saturday's ITV live show by Scotland's Leon Jackson.
But as the complaints shot up, ITV revealed Leon won by 10% of the vote and called it "fair and square".
Leon's mother also claimed many of her son's supporters were also foiled in their attempt to phone in to back him.
There had been 80 complaints on Monday, but the number shot up above 1,500 by Tuesday.
Some of those said they tried to vote dozens of times but could not get through.
Before Saturday's final, Rhydian was clear favourite, but he was pipped at the post and to a £1m recording contract by Scottish crooner Leon, who sang a duet with Kylie Minogue on the live show.
A stream of Rhydian supporters contacted the BBC to complain that they could not get through and some radio stations in Wales said they would boycott Leon's single and demand a recount.
Welsh First Minister Rhodri Morgan revealed he was among those who tried to call in "as a loyal Welsh person" but failed to get through.
But ITV said while many Rhydian fans were disappointed, "the simple fact is that Leon won the X Factor fair and square".
The broadcaster said Leon "performed strongly across the series and was the outright winner on the night by a full 10% of the vote," although there was just 1% between the finalists before they sang their versions of the new single When You Believe.
ITV said it never normally revealed results but it wanted to clarify Leon's winning margin "to reassure viewers on this occasion."
Leon told the BBC he felt he would be under closer scrutiny now: "I went and gave my best performance. You never know how the public is voting and that aspect of things is out of your hands," he said.
"I just feel it's extra pressure now because I'll be under a lot of scrutiny and there's extra pressure for me to do well and produce really good stuff. I just want to give the public back something because they are the ones who put me in this position."
Supporters of Leon also claimed they had been unable to vote for him.
Leon's mother Wendy Jackson told Glasgow-based Real Radio lots of people texted her to say they could not get through.
"I even had one person tell me they had tried 300 times to get through to Leon on the landline and they couldn't get through - so it's not just the Welsh folk that the lines were jammed, the Scottish ones were as well."
X Factor production company Talkback Thames blamed the engaged tone met by some viewers on the volume of calls. Some Virgin Media customers had problems, but that company said it had not found anything unusual so far.
Meanwhile, Rhydian's uncle denied they were disputing the result, "because we don't want to sound as a family churlish or that there's any sour grapes".
Nigel Roberts told BBC Radio Wales Rhydian was due to sign a recording deal this week and hoped to do a tour.