Partial settlent

System

Ok, i have today had a letter from pra group. They have supposedly bought the debt from natwest. They are telling me to not pay wescot anymore but pay them instead. They are asking for the full amount originally owed. I have a letter from wescot dated the 7th of feb 2019, stating that they have received my partial settlement and that the account has been handed back to natwest, who agree to not pursue the remaining balance and not to pass the debt onto anyone else to pursue. The letter fro pra group states that they purchased the debt on the 8th of feb 2019. I guess there fishing for an easy target? However i replied via email to pra group, attached a copy of the letter from wescot. I told them i also have an abundance of emails from wescot confirming that i would not be liable for the remaining balance if i pay the agreed settlement figure.