I get the feeling you don't want to deal with them because you are trying to hide something.
If you aren't, taking ten minutes to write a letter and send it by recorded delivery is the only way to stop them contacting you.
When a person dies his debts have to be paid from his estate. This is the duty of the executor, or next of kin. If the deceased left absolutely nothing, then it is the executor's duty to inform the creditors.
Nobody can inherit what the deceased did not have. If he had �1000 but debts of �1000 he has nothing to leave.