Not sure what country you're in, but here in the UK the law is on your side.<p>* Get everything in writing. Keep copies. Inform both MS and the collection agency that they're in error. Send it recorded. Make them sign for the letter.<p>* Next, ignore them until they either take you to court, or put something on your credit record. Only a court can force you to pay a debt like that.<p>* If they take you to court, you have a period of time to respond. You don't need to physically go to court in most cases.<p>* If they put something on your credit record, take them to court to have it removed. That costs about £70. The record comes off in a matter of days.<p>* Any court judgements issued can also be overturned, if you have a good reason for not responding in time.<p>* Any costs (eg that £70 above) can then be reclaimed through small claims. A small claims filing costs about the same, but you just add it to the claim you're making. Add on postage, travel, etc.<p>* Remember the judge will recognize the sleazy agencies. (They will probabaly deal with several such cases every day). If you have the proof in paperwork, they will find for you.<p>* Once overturned, they cannot take you to court again for the same amount. If a judge decides the amount is wrong, you cannot be harrassed again for the same amount. End of story.<p>You've probably now lost the money however since you've essentially admitted fault, but you may be able to put it through small claims. Not sure.