Capital Management Services, LP Debt Collection Complaint

Capital Management Services, LP Debt collection department,

Cont'd attempts collect debt not owed Debt is not mine California

I have been receiving letters and calls from - funding about a debt they claimed I owed. A few years ago, I asked them to provide proper validation that it was mine ( a statement from the original creditor or even the signed agreement that I signed up or agreed to the credit ) but they could not do so, so I requested they remove the collection from my credit report and they did. Then it looks like they sold that debt to Capital Management Services , LP and they are now claiming I need to pay THEM. When does this end? The alleged debt from what - told me, was from YEARS ago supposedly ... is n't there a Statue of Limitations on how long they can keep contacting me and threatening me to pay them this debt? Please help ... this is not mine to owe.