I have had no extent of trouble with trying to cancel with ADVFN.
I initially upgraded to a Silver subscription in early August only for the service to cease to work for me (it wouldn't work in Internet Explorer 9, Firefox 6 or Google Chrome). I tried for a few weeks to get this working again (including emails to their support desk) but to no avail.
I then tried to cancel with them, which is still an ongoing exercise in seemingless futility. I initially sent the required letter to cancel in late August. There was no reply to this and I was once again charged the monthly subscription. I followed up in mid-September by email to find out what was going on and was told that my letter had not been received and that my emails (including scans of said letter posted) would be ignored in regards to cancellaton.
I dutifully sent a second letter in mid-September (with a copy of the first letter) to again confirm cancellation and complaint that the service had not worked since mid-August. Once again I heard nothing back but again was subsequently billed the next two months.
At this point, I emailed once again to find out what was going on. Again, I was told that my letter had not been received. I dutifully sent them a third letter (including copies of the first two letters) and a further email with copies of these letters too. Funnily enough, this third letter has not been received either. Having worked for Royal Mail, I know the chances of three letters to the same address going missing is next to non-existent.
Currently, I have been in contact with my credit card provider to reverse these charges. As a precautionery measure, I have also had to cancel my existing credit card in order to ensure that these unlawful payments cease. Despite the numerous letters and emails to ADVFN, I have heard nothing about my complaints.
Frankly, ADVFN has been an odious company to deal with and has disgusting levels of customer service. I can only advise to stay well clear of them and their outdated and clearly duplicitous practices.