How do I switch off my Veva 1210 answering machine?

I use BT's 1571, but have recently eviiently partially activated Veva's Answering Machine.The icon flashes and callers are told they cannot leave messages. The Veva mechanism inhibits BT's version so my, bcallers cannot leave messages. I wish to re-enable my BT Answering Service.y switching off the Veva 1210 version