Mortimer Clarke and Resolvecall

[Kev64]

I recently got a letter from Mortimer Clarke stating they were going to send to my house a company called Resolvecall reference a debt i couldn't even remember having. I then got a letter again from Mortimer Clarke stating what the debt was for which i estimate is between 11 and 13 years old. I was unaware it was still in existence and had completely forgotten about it. They also said they would send Resolvecall around. Today i received a call to my door from Resolvecall who wouldn't take no for an answer and still dropped a note to contact them through the letterbox. Is there anything I can do to stop this happening again . Any advice would be greatly appreciated as this is stressful and worrying. Thanks