Conventional memory technologies are facing device physical scaling issue. As one for the most promising candidate for future non-volatile memories, resistive random access memory (ReRAM) with simple two-terminal sandwiched structured devices exhibit attractive performances. We demonstrate highly stable and reproducible atomic contact based quantized conductance states in Al/Niobium oxide/Pt resistive switching devices. Three levels of control over the QC-states, required for multilevel quantized state memories, like, switching ON to different quantized states, switching OFF from quantized states, and controlled inter-state switching among one QC‑states to another has been demonstrated by imposing limiting conditions of stop-voltage and current compliance. When the top electrode of the device is changed from Al to Nb, the behaviour also changed from abrupt to gradual (analog) switching. The conductance was found to be changing gradually and continuously with subsequent voltage pulse signals, which are exploited to demonstrate spike rate dependent plasticity emulating short term memory and forgetting analogous to remembering and forgetting processes of biological synapse.