Did not leave message despite answer service stating all calls other than telemarketers will be called back, speaks for itself

Caller: Some mob representing a solar company.

This number has called me AT 6 times in the last day or so. I was letting it go to voicemail but no one would leave a message, so I just ignored it. They rang again today (5.25pm), so I thought I'd pick this one up to see what it was. Turned out that I made the mistake of showing some interest in some solar deal, so they were ringing to follow up. "Thanks but not interested". Hung up.

This number called me FIVE times in a 4 hour period. Phone rang. Came up with this number. Went to voicemail. No message left. I am on the "Do Not Call" register, but it obviously makes no difference.