Complex coefficient filters (CCFs) are widely used for phase-locked loop (PLL) in three-phase power systems, while its usage is largely sparse in the single-phase domain. Single-phase CCF-PLLs so far reported in the literature do not yield satisfactory performances at off-nominal frequency conditions, which is a crucial PLL attribute. Whether they are a suitable filtering technique of choice for single-phase PLL is yet to be formally documented in a methodological way. In this regard, this article derives an enhanced version of the single-phase CCF-PLL (ECCF-PLL), which is able to provide accurate estimation of grid parameters in dynamically changing grid frequency environment. The proposed ECCF-PLL is then numerically and experimentally compared with few other single-phase PLLs to gauge its efficacy and suitability. The test shows the advantage of harmonic robustness from ECCF-PLL, which is specifically useful in a weak grid