forecast demand,
maintain MPS.
review MRP,
rescheduling and expediting
are the major responsibilities of planners.
The problem you are facing is a systematic problem of your company, which can not be solved simply by the effort of only yourself.
A whole system must be set up to measure customer satisfaction such as CRD (customer request date) performance of both internal and external customers. Also the performance management will also need to conform with the customer satisfaction indicators.
Simply put,
1st, the company will need to identify its CSF(critical success factor)
2nd, to achive the CSF, KPI(Key Performance Indicator) such as the CRD need to be set up to measure the the CSF to see how well the company does
3nd, reengineer process to faciliate the achievement of your KPI
last but not the least, top management must be involved very actively to EXECUTE.