I owe over a $1000 and is in final collection

Email Subject say "Wages CAN BE Garnish."  It says "Closing amount to Freeze Down this case file by today - $850."  It says my case file is HM/27A/98-36471 with ACS .  It says "after sending several email we were not able to get hold of you."  "If you do not take immediate action we will be forced to download this case against you and once it is downloaded the creditor has entire rights to inform your employer regarding this....found guilty ...then you have to bear a lawsuit which will be a penalty of $4515.85 and your bank account will be closed."  I have NOT received any email from them before plus I don't owe that amount of $1385.00.  What should I do?  It scares me.