Did some changes and managed to get it to work, I now populate my data by using 2 comboboxes, the latter is filtered by the first, by adding a event listener on the first combobox, so whenever something is changed in the first combobox, the latter combobox will get filtered.
sender, RadComboBoxSelectedIndexChangedEventArgs e)
//dataset here / datatable
"column you wish to show in combobox"
//Then Finally clearing the combobox text or as in my case I decided to select the first item in the dataset instead.