"Impossible to get through on maternity phone line"

I have spent hours trying to get through to someone on the line given to me in my ante-natal letter to change the appointment. The line is either engaged or rings out to be hung up on. On calling the main St Mary's switchboard, I am told it is the only way I can change the appointment. There needs to be better phone support or the option of email communication so patients can contact the ante-natal department.

The number in question is: 0203 313 5370