Hello! First of all, my advice to you is STOP PAYING THEM. The loan will never end. That's the point of this scam. The moment you accede to their demands, that's where they get you. Secondly, they won't come to your office. They know better. Based on what you have told me, and if you haven't said anything to cause them anger, you're most likely not worth them paying anyone to go anywhere to harass you. The most they will do is send you videos of their runners setting fires to some poor chap's house or other such scary videos (which I have been receiving but have yet to open because my heart is too small...)
Secondly, close your bank account immediately and report it to the police. If your bank account is still lying around and making transactions to them, you're most likely interfering with current police investigations and you might be implicated, as I was recently enlightened by a very angry IO at the police station.
Thirdly, lie low and ignore/block their calls and messages. I wish you all the best. Please PM me if you need more assurances.