IF.....you have a simple modem.....not a modem/router or gateway type of device.....AND....you also have a Static Internet IP address that is assigned to you by your Internet Service Provider (ISP).....I may be able to help with access from the Internet to your 802.11ac Time Capsule drive, or a USB drive connected to the Time Capsule.
But, port mapping can be complex, so there are no guarantees that what works well for me, will work well for you.
Might be able to help if you are trying to port map to another device on the network if you are very patient.