Antes de mais obrigado!
Até me sinto envergonhado em dizer que a solução esteve sempre à minha frente

era o parametro nome que eu não estava a mudar!
Parameters
chart_id
[in] Chart identifier. 0 means the current chart.
name
[in] Name of the object. The name must be unique within a chart, including its subwindows.
type
[in] Object type. The value can be one of the values of the ENUM_OBJECT enumeration.
nwin
[in] Number of the chart subwindow. 0 means the main chart window. The specified subwindow must exist, otherwise the function returns false.
time1
[in] The time coordinate of the first anchor.
price1
[in] The price coordinate of the first anchor point.
timeN=0
[in] The time coordinate of the N-th anchor point.
priceN=0
[in] The price coordinate of the N-th anchor point.
time30=0
[in] The time coordinate of the thirtieth anchor point.
price30=0
[in] The price coordinate of the thirtieth anchor point.