Called, hung up when I answered then called again. Asked to speak to the Three network account holder. Identified company as 'Sprint Communications'. Tried to sell me a renewal on my Three contract (which is up in November) and a new phone. When I said I wasn't interested in renewing my Three contract he offered to transfer my number to a different network. I pointed out that I already have a phone on a different network (some years ago my sister chenged to Three and I worked out it would be cheaper to have a phone on that network than to call in from my normal phone, she's now going back to the same network as my normal phone) and wasn't interested in keeping that number. He tried to sell me a contract on another network again. I repeated my reasons for not wanting to move to another network and after a while he accepted it.
I pointed out that the number was registered with the Telephone Preference Service (TPS) so, as I have no relationship with Sprint he should not be calling me. I asked him to have my number removed from their systems and from any lists they sell on or use. He said he'd try.
Also reported this on Who Calls Me.
Now I'm off to shop them to the ICO. I suggest others do likewise if they get a call on a number they have registered with TPS.