Citizens Advice said its poll found 92% of people do not trust sales representatives who cold-call, describing the findings as "indicative of marketing that is nothing more than a nuisance".
The advisory service is calling for financial services firms like claims management companies and debt resolution services to be banned from cold-calling to protect people from unscrupulous operators.
Research last year found that the most common unexpected sales calls, texts and emails made to households in Britain were related to personal injury and accident claims, energy suppliers and double glazing firms.
Companies selling debt relief services, offers for extended warranties on products and firms selling ways to unlock pensions were other regular offenders, as reported to Citizens Advice. It found 67% of British adults, equivalent to more than 30 million people, had received an unwanted telephone call, text, email or letter about claiming for mis-sold Payment Protection Insurance.
Citizens Advice chief executive Gillian Guy said: "A ban on these firms would help people know a call out of the blue is one not to be trusted."