I chose monthly billing because I thought it would not last long. I wanted to build a similar service and app myself. I would never have dreamed that it would be a deal with the devil – the kind you can never get out of. On October 15 I blocked 3D Secure on my account so that they could not charge me anything more. Then I wanted to settle it amicably with them, and on one of their hidden-away pages I found that I could only cancel the service by phone, on a number that “ends” in the USA (+1).
I sent all my details except the password to my cousin, who speaks excellent English and Czech. She called them, but they brushed her off: even though she knew everything, she was not the owner, because I had stated that I am a man and the caller was someone with a female voice. Anyway, they are welcome to delete the account or do whatever they want with it, there is nothing but junk in it. The emails they sent me: 
Yes, you are seeing that right. I am getting messages from an automated system, from support, even from the CEO. And in the end they offer me a monthly plan of just 4 USD instead of 10 USD. I still do not want it. Never again anything from them, this is not how a reputable company behaves.