I've had mobile operators call me with offers around renewal time but never a broadband ISP. I think their preferred tactic is to keep quiet and hope we forget about the end of the contract/introductory deal and subsequent price hike.
I tried to haggle with my last ISP, whom I was paying about £9 / month for standard adsl2+ broadband (including line rental) but they could not match the BT incentives of a £125 prepaid card, plus another £120 from topcashback which brought the VDSL price down to around £15 / month net.
Are you instead suggesting you get calls from other ISPs after just visiting their site whilst researching a new deal? That's never happened to me - I don't register my contact details with an ISP until I'm ready to sign up. I'd find it worrying if their traffic analysis managed to link my reseach browsing to my personal details via some third party so as to trigger a sales call.