Vertex and MBD both trying to collect same prescribed debt

Vertex could you please stop contacting me claiming they collect for their client MBD. On the other hand MBD sent someone to me at work last week so that I can sign to acknowledge the debt. I refused even to read let alone sign. I told the man that the debt is prescribed. After some argument that man agreed that the debt is prescribed and they are aware so both Vertex andMBD are taking chances. There is no way three companies are trying to **** me by collecting same prescribed debt. Vertex is not even appear on my credit report.