You don't know how they got your number nor do you want to buy the rubbish they're selling.
Thankfully there's now an app to screen and block nuisance calls to your mobile.
The TPS Protect app allows customers to register which the Telephone Preference Service (TPS) and log complaints about nuisance and scam calls.
With the free app installed you can see the TrustScore - the consumer rating - of the company calling you so you know whether to answer or cancel the call.
For an extra 99p per month, once their free trial expires, users can block unwanted calls by diverting them to voicemail. They can also create approved and blocked lists.
You can tailor the types of call you are happy to receive, for example blocking the majority of unwanted calls by setting your TrustScore to five, but still receiving calls from specific groups, such as 'charities'.
You can register NOT to receive unsolicited sales and marketing calls by joining the TPS register.
If you're on the register companies making cold calls must cease unsolicited communications with you within 28 days or face prosecution.
The service, funded by the direct marketing industry, is free to join.