Line transferred from BT to Sky 2 weeks ago and since then have had intermittent dialling tone (just like "voicemail waiting" tone on BT). Handset was also flashing Voicemail waiting lamp.
Have dialled 1571, and also used the Voicemail press button on the handset and announcement states there are NO messages.
Have disconnected handset (BT Big Button+) and replaced the batteries - this stopped the lamp flashing however the dialling tone is still intermittent.
Tried ringing Customer Services twice but gave up each time after extended on-hold (do tech support work weekends??).

Anybody who can offer advice - would be most grateful.