Let me understand your issue
The plugin expects the file and images to be in the folder in an unzipped format
And you are saying that you get file files in a zipped format?
And are you saying that within the zip file the [filename].blm is not a fixed name e.g. [randomnumber].blm?
Are you also saying the directory is something different from /wp-content/uploads/rightmove/ ?
Have you checked to see is the sending system can have the option not to zip?
What is the name of the agent system for my reference?
Once I have a better understanding of your problem I can see if I can help you.