Refresh means something different in the case of offline CUB files in Excel. Short answer, is don't use refresh, but simply change a slicer in your query, that'll cause Excel to repull the data. There is macro code out there that demonstrates how to force a refresh without actually changing the slicer, but be warned it's generally a little incomplete. (Putting on the finishing touches of my own extension now.)

Excel treats the CUB file more as a type of "cache", rather than the offline cube it should be. CUB files seem to be depreciated, with no replacement in sight. (Pity). I highly recommend that you consider purchasing CubeSlice, since it does a much better job of creating CUB files (use the ASSL model only). Again, it's not a perfect solution, but the best available.

In general, avoid any strategy that relies heavily on offline CUB files, since it's not well supported. You'll run into limitations and performance problems in many instances.