In case you need to cross check the amount received for Mews Merchant card storage on your invoice invoice, you could do it directly in Mews Commander.
Open side Menu Bar -> Finance -> Credit Card Report
Dates: Full month of invoice dats (i.e. 1/7/2017 00:00 to 1/8/2017 00:00)
In the received report you would see number of cards created last month next to title "Credit Card (102)". Number in brackets is the number you could multiply with your storage fee and you should get invoiced amount.