So sorry that happened to you! It's always a huge bummer when you put your heart & soul into a cake and then SPLAT! It crashes!! : )
I noticed in your post that you said the cake kept sliding... did you put the second tier on top of the first tier that was cut at an angle? Just wondering because I made my first topsy turvey cake a few weeks ago - I followed the tutorial on CC, and the best way to do them (so I've read anyway...) is to cut your tier at an angle, and then cut a circle out of that tier, big enough for the next tier to fit into. Make it flat so the tier sits flat inside that cut out circle. As long as you use cake rounds under each tier, and dowels for support it should be just fine
I think you can find the tutorial under the ARTICLES section here on CC, I just searched for Topsy & it came right up!