Check the D-Link site, I think your model requires port forwarding.

Also, after installing any software or updates, always do this SAFE Boot & Repair Permissions.

3rd point is ... your ISP .. don't they also have another name .. I have a suspicion it's the same company as OOL (Optimum OnLine or something like that) that are reknown for picking on p2p users. No easy answer but in some cases changing port to a very high one sometimes works; ports 49152 - 65535 such as 64049.