Hello,
I'm sorry to hear about that. Unfortunately, there is no refund or any way to get the items back due to a bug causing this, unless you have a valid proof of it.
If you got kicked while combat-tagged, then unfortunately you will drop your inventory and it might have despawned or picked by other players.
If you got kicked because of glitch or there's something odd about how it happened, you can make a bug report like
bobsilowski
said above, with evidence if can.
If you got kicked because of lag/ bug/ glitch, some tips I can give:
1. Use 1.8.9 if haven't, as it's the recommended version and have less bugs.
2. If you experience lots of lag, try these
tips.
3. Keep your cps not too high, less than 20-30 cps is better.
4. Avoid glitches, for example glitchy places like fences or glass panes.
That's all I can tell, if you have any questions feel free to ask. Hope it helps.
Enjoy playing, and good luck.