So you had $40 deducted from your account for how long? what subscription did you have? If you go to your settings on your device- click on your name where it says apple ID and Icloud Itune App Store etc.
youll see names and passwords then payment and shipping and the 4th one down will be subscriptions. click on that and that willl tell you what your subscribed to. If you did not subscibe to any of these i suggest 100% calling apple customer support for app store/subscriptions becuase if you just dispute it, they won't allow you to even download apps anymore. If you call them tell them your situation, they will most likely give you 1 maybe 2 months of a refund- depending on how long it was going on for. hope this helps!
https://getsupport.apple.com/?caller=cups
this will let you chat with someone or schedule a call. just select your issue