Unbounded hint growth, truncatehints not working

one DC has big sized hints(467G) and will use up the whole directory sooner or later and we need to delete it. I ran nodetool truncatehints but it's not working. I see from nodetool tpstats there is 2 active hintedhandoff and 40 pending as follows:

HintedHandoff 2 40 0 0 0

it seems like there is an issue with hintedhandoff which is hung and caused nodetool truncatehints not working.

please advise!

Thanks