Spoken about Martingale, I found a website that wrote in their terms they would confiscate your funds and close your funds if you use systems like Martingale.
Why would they do that? it is just a strategy, not a way of guaranteed money.
I assume its fine to use this strategy?
Using the Martingale system is not prohibited, (the bookmaker can only limit the maximum one-time win or bet) it is everyone's right, and I suspect the site you are talking about is full of shit even without this silly restriction. In addition, as far as I know, the use of the Martingale system in the long term is too unprofitable.