The Pontypridd men had spent Â£230 (300 euros) on the accommodation before realising their error in France.
It was one of the many travel issues the Football Supporters' Federation (FSF) Cymru have been called on to help with.
Vince Alm, of FSF, said: "We were trying not to laugh."
He said the men turned up at the FSF fan embassy in Lens, ahead of Wales' 2-1 defeat to England on Friday.
"They were looking for the Lens Switzerland Hotel," he said.
"After further investigation we found they'd actually booked the hotel in Switzerland and not in Lens.
"They had to lose their 300-euros-a-night and go and find something in Lille."
He added: "The one was blaming the other and we were trying not to laugh because it is a lot of money."
Mr Alm said there had been a lot of "good stories" relating to travel mishaps during Euro 2016.
The FSF had to help 40 people who lost their coach to the UK in Lens.
"A lot of them stopped to have a drink, maybe, or got themselves lost. And we had to assist them to get back to Paris and back to the UK."
He said French police had also opened up a cell at a police station and allowed a fan to sleep inside with the door open because he had no money and nowhere to sleep.
And there have been several fans who have fallen asleep drunk on the street who have been taken to hospital.
The FSF have also alerted the authorities when fans have gone missing in France.
"But we managed to get them all home and that's our job - to assist fans," he added, saying they have not had any "serious incidents".
As Wales face Russia in Toulouse in their vital third group game on Monday night, fans face uncertainty as to if, where and when the team will next play at Euro 2016.
The team could still top Group B or crash out of the tournament.
If Wales qualify for the next round, the permutations mean they could play in Paris or Lens on Saturday, Lille on Sunday or Nice on Monday.
With regards to ongoing travel, Mr Alm gave this advice: "Make sure you have it [your arrangements] done by Tuesday because the prices go up.
"All these hotels are pre-booked in the different cities by the footballing authorities and just people taking a punt.
"So, as soon as you know, get your travel plans in."
Two Welsh football fans accidentally booked a hotel in Lens, Switzerland, instead of Lens, France, for the team's Euro 2016 game against England.