Your friend has only one option left and that is, to stop paying once and for all. If he carries on, either he will run road or jump. End of the episode, his house will also kena paint.
Info on sui debtors is a precious commodity in the moneylending biz. More so, for the unlicensed ones. The sui debtors particulars can be obtained quite easily. The info is always sold to others. Once your particulars is with a licensed ML< there is no way to stop them from passing it around to licensed as well as unlicensed moneylenders. It could be a staff in the set-up that wants to make extra cash. For all you know, the boss of a licensed moneylender could also be involved in unlicensed ML business.
The unlicensed ones, 'faceless' and usually based overseas, adopts the MO you mentioned. When last payment, they will tell debtor no account to bank in. Sometimes, they purposely don't answer your call and will later accused you of not calling them.
These 'faceless' ah longs are the ones creating the many problems you read in the newspapers. They have nothing to lose. They play on your fear factor. It's machiam 'face-off'. Once you are not afraid of house kena paint, you are the winner. They may or may not execute the job, depending on several factors. If you 'hiong' them, they sure do it. But if they already made a pile from you and you refused to be further bullied, 50-50.
My friend once approached me for advice. He took loans from licensed as well as unlicensed moneylenders. One fine day, a stranger SMSed my friend asking for final payment of a loan. My friend 100 sure he never took from this chap. But upon being threatened, my friend gave in and transfered the amount. He then quickly changed handphone number. No point. Same chap called again. Again, my friend paid up. No idea what's the status now coz I don't have his handphone number which keeps changing.