You should persevere by dialling 150 from your Virgin landline and choosing the thinking of leaving option. best time to call is first thing on a morning, they open at 8am.
Cancelling the direct debit would not cancel the Virgin account, you do need to speak to retentions or send a letter to them via recorded delivery
Virgin Media Sales Operation Support, Diamond Plaza, Daleside Road, Nottingham, Nottinghamshire, NG2 3GG
Dave
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali