I have two lines under this account. 

The second line has been cancelled two months ago.

And both month, I am being charged with Easy Roam.

I would recommend you download the PDF bill in self-serve to see the date of the roaming fee. Normally roaming fee of previous billing cycle is transferred to the next one. 

The date of the charge would show up in the PDF bill  and you can check if it is before or after cancellation date.

Hi ​@PeterW Lee, any pending roaming charges may take up to two billing cycles to appear on a bill as it can take some time before they are communicated to us by our roaming partners.

We looked into the charge you mentioned and if you are referring to the line ending in *88, it was charged for roaming only once on your most recent bill, with the date of the charge occurring before the cancellation date. 

The charge was triggered by data usage while roaming and is valid. You can check the usage in your self serve.  Here is more information on how to avoid roaming charges while travelling https://www.koodomobile.com/en/help/understanding-how-youll-be-charged-while-travelling