I have tried the suggestions mentioned in This Famous POST but unfortunately ain't working out form me.
It gives me an error:
Error: Authentication failed. Error:
Critical error: Could not connect to server
I don't know what went wrong, I have created a new key pair(.pem file) since I couldn't find any way to download the existing one that needs to be added to Filezilla.
Make sure that the same .pem key-pair (that you are using to access the instance), has been used while creating the instance. In your post, you have written that you created a new one as you couldn't find the old one. This will not work.
If you have lost the old .pem with which the instance was created, then you will have to create a new instance using the new .pem key-pair file.
PS.: Do not loose the new one. :)