There are a few sites that you can go and double check.
Steemspectacles is the one I use as it shows you which users have commented on or engaged with you over the last 100 days. It will show you active followers ,dead followers and ghost followers.
The other site is Steemagency https://steem.agency/follower/followers and it will give you the details similar to steemspectacles.
Don't be alarmed by how many dead followers you have as we all have them and a good guide is if you have 1000 followers you will find between 10 and 20 % are genuine and alive. The other 80% are dead or have left the platform and will be back hen the Steem price rises again.