Caller: Claim to be NBN

Indian accent claiming to be NBN to tell me there have been fluctuations in my speeds and they want to fix them. Had recently run a speed test myself and advised them of the figures and there was actually no issue - that's when they hung up on me.
Complete scam as not giving them access to my system.
These people have also called from other numbers claiming the same thing. All numbers have come up with no previous comments so must be cycling through different numbers all the time.
These people need to be stopped.