How to stop the third party payments from happening

Every time I top up the recharge on my phone, about 6 euros get deducted from some third party service without my knowledge and without my consent. I have found no way to block these payments. It is difficult to catch an english speaking customer service provider which is why I have not been able to directly ask O 2 to put a block on these payments and I cant find how to do it myself from the website as I see no such option listed on the website/app. Some guide/instructions for the procedure to block all the third party payments would be helpful.