Stop sell on normal PSTN connections, also probably just an Openreach third party agent.
Try switching the HH off and unplug it giving it a few minutes then replug it in and switch on again. If it doesn't turn blue (allowing about 3 minutes) use a paper clip to press the Hub's factory reset button. If this doesn't fix the issue, contact Customer Services on 0330 1234 150. They are available 8am to 8pm today.
RIC9380 😊