I would like to get a refund for the wrong EA.

 

As you can see, I mistakenly paid mt5 for what I had to buy in mt4 version,

and I tried to contact MQL.com, but there seems to be no such request system.


I activated it already, but I didn't even use it.


How can I be guaranteed?

 

As far as I know - the refund is possible in case you did not activate the products and you canceled it within 7 days since purchase date.
But as you already activated so no official refund.

You can only write to the service desk (tomorrow, or today evening because they are fixing something) asking them for advice (just tell them that you mistakenly bought tool for MT5 but you were/are going to buy same/similar tools for MT4).