Not responding to them is the smartest way out! We can't eradicate such people because steemit is such a platform where one needs the mutual help and the easiest way is to scam like that. 
I feel that one should make build longstanding relations with the fellow steemians rather than making upvote for upvote appeals !

we cant stop them directly but we can give flag to them so that the steemit people can track them and also i have face an issue whenever i give them flag they downvote my blog

There is no direct way to stop someone on steem for anything since there is no censorship built into the blockchain. however we can do a few things that can discourage them

1) Flag them which will help some powerful whales to track them if needs be.

2) We can ignore them completely. once they see that their efforts are not being met with a respnose they will stop doing that and instead use the same energy to write better comments. 

The short answer is.... You can't. but first;

Congratz!

You've become noticeable enough to garner the attention of vote beggars. 

"hello, i vote your post, please vote mine"
"Kind sir, please read my post
"If you want me to follow you, please follow me"

The Steem blockchain is Borderless and Permissionless as a Content platform. While it is a good thing, that entail unsavoury (or sometimes unsavvy) people doing unsavoury things like asking for votes.

Trust me, I get on average 10 to 20 such messages a week from people like these on just about any avenue they can get a hold of me.

After some time you pretty much just have to tune them out. There is no platform wide censorship to stop these activity, maybe you can spare some vote power to flag them in the comments? or if there come at you on telegram or discord you can block them? It's going to be a perpetual whack-a-mole  game though..

Have fun!!