Company claiming registration charges without any pre-info what to do

 My query my son had just turned up 18. He registered himself into an private home based typing job conpany .they tricked him into an digital agreement and are now asking for there registration charges and continuously sending mails regarding they ll file a complain and all that . They are saying ur son has signed an agreement he failed to submit his work on time and he ll hv to pay registration charges as told earlier . My son told me on phone they gave him incomplete information and then they sent a link through mail to agree to terms then they asked him to click on the link to get terms and conditions . But later on he automatically got this mail that he has signed an agreement with their company and all that now they are saying it was digital signature , i dont understand what type of digital signature it was . Now they are asking the amount and continuously sending mails regarding that.