Being threatened but no valid proof of the claim

So I've been handed over by Europcar to LGR to collect money owed to Europcar. I have asked for proof of the claim from Europcar as how can I be handed over without knowing all the facts and validating what their claim is. I was forced to pay the attorney fee otherwise I was going to be blacklisted for not paying their fee. Now I am being threatened that I will be blacklisted if I do not pay the total amount TODAY! How can I be blacklisted if the claim has not been validated or verified. Europcar collections don't answer their phones because i've been calling for weeks, nor do they respond to emails. LGR doesn't answer calls either! So how am I supposed to resolve anything if I can't actually speak to anyone. Is threating someone without them providing evidence even legal? No proof provided to me by either party yet I am expected to pay. Pathetic! Even the number of the sms for LGR doesn't exist, the number listed online goes to VM no matter what option I select. Get told to hold for an operator since Europcar is not one of the companies on the main selection, yet no operator answers and go back to the IVR to select any company. Go to team-leaders VM, leave a msg with details, date and time to get a call back...NEVER HAPPENS!!! So what now, pay pay and pay more...This is more like ****************