Most lenders borrow money based on risk projections and as such, an account that then falls into default becomes problematic for them to collect monies from and therefore it may be more commercially viable to pass it onto another firm who have a different business model, which allows them to purchase debts, and collect with their own techniques.
When you sign a credit agreement with a creditor, there will have been a clause within the small print of that agreement. The creditor will have stated that they are able to assign their rights to a third party.
However, just because a new company has taken on the debt, as per the terms of the notice of assignment, they are not allowed simply to bull you with letters, text messages, or phone calls. If you're being threatened by any creditor, new or old, and have unaffordable debts - give us a call on 0141 221 0999 for free, confidential advice.