如何投诉卡塔尔航空公司？
我今年2月1日在卡塔尔航空官方网站上购买的经济舱Value机票，该票注释为改签免费。但2月16日我在官网上改签机票时，他们却强行收取了我们4000元人民币的罚金，否则无法改签成功。
我已经通过电话和邮件向卡航说明了情况，但是他们的回复是：在我改签时既然已经支付了罚金，就等同于同意了该条款（我们的英文不好，不知道是否理解他们回复的全部内容）。现在我还想知道，还有什么方法对他们做进一步的投诉？
谢谢！
附卡航的回复：Whilst we remain concerned to learn of your disappointment with the outcome of your feedback, kindly be advised that according to the report we received from our E-commerce team, you were received an Email which contains the flight confirmation, E-Ticket and Fare rules which has the change conditions to your E-mail address, The report further states that You have and accepted the terms and conditions online, then you received the confirmation.
Kindly note, as per Qatar Airways Conditions of Carriage, passengers who wished to change any aspect of transportation in the ticket, is subject to conditions, prohibitions or restrictions on refunds and changes.
We would like to take this opportunity to inform you that each travel class has different fare classes having its own fare levels and conditions relating to ticket or reservation restrictions. The booking terms, conditions and fare rules will apply upon any change in a ticket. In the event of change of booking, kindly note that in addition to the applicable change fee any additional fare difference as per the prevailing fare on the new date of travel would apply.
We appreciate the opportunity to correspond and to explain the matter with you.
其实当初你在收到卡航要求收取改签费用（不是你所描述的“强行收取了我们4000元人民币的罚金”。强行？航空公司能强行从你账户里面取钱？）时，你就应当立即进行投诉，并且附上能够证明“经济舱Value机票，该票注释为改签免费”的相关材料。
……然而你并没有这么做，而是乖乖交钱……这在对方视为你已经接受这份要约。事后再进行追索，除非你能提供完整的证据链，否则很难从理论上驳倒对方的。追问
我们当时在国外，改签遇到问题时我们立即电话联系了卡航北京办事处，但因为是春节期间，一个电话号码没人接，另一个电话号码联系了两次，都没有把事情叙述完就忽然中断了（400开头的电话号码主叫是每分钟3欧元）。而不支付那笔罚金，我们就无法完成改签。
追答以后一定要记住，类似于投诉、通告、与店家/卖家/销售商进行比较重要的通话时，尽量开启手机录音，事后可以作为证据。
从目前的情况下，你除了持续投诉外，也实在没有什么进一步的证据了。从航空公司的角度而言，你的投诉内容都是主观描述，而没有客观证据，也不太可能对你进行任何道歉或补偿。