Thankyou!

Hi I'm asking for a bit of advice as I'm helping my dad out, who has recently set up a small business. He was contacted by Foresters Fund For Children/Vision Publications Group who I now believe to be Vardis. He agreed to an advert in their Class M8 magazine. After that realised it was a [problem] and sent a recorded letter saying he wanted to cancel. They said he couldn't as the 7 days cooling off period had elapsed. They also have an audio clip of him agreeing to the advertising. He has now been invoiced £178 which we are holding off paying as we have seen on the internet that its a [problem]. Now not sure where we stand... any help with this one would be appreciated! Thanks