In that case the agents are wrong from my point of view. There was a change in the t&c, that the customer has two alternatives:

Alternative 1: Only the taxes and fees are refunded. Miles and airline surcharges are not refundable. Free of charge.
Alternative 2: Full refund of miles, airline surcharges, taxes and fees. Charge of EUR 50.

So if you've paid a charge of EUR 50,-, they have to refund all miles, airline surcharges, taxes and fees.

You find M&M's t&c here.