False Advertising or Staff not equipped

So my issue is this : The following add when i joined my son who is 11 on the 15th was told he had to have Vitality and got 30 percent off however th add at the time said the following : Children under 18 Can Join virgin active for 50 percent off the standerd monthly fees if you or your spouse use the vitality gym benefit . My gym at Honeydew told me this is not the case even though i showed them the add . Please advise this to me and i many be corrected is false advertising . Please virgin active please correct this with me and any other client that has joined during this time . My son Joined on the 18th of January i have a screen shot of add with date on it which i also showed gym staff and management .