If you are asking this question, you have most likely been labelled as using computer assistance against human opponents in rated games.
You may use engine assistance against Stockfish, or against a human in a casual game with their consent. In no circumstance can you use engine assistance in a rated game. If you do, even by accident, you will be set as a cheater.
Alternatively, if you were sandbagging (playing at a lower level than your 'real' level) you may also be set as a cheater.
Alternatively, if you used other accounts (sockpuppeting) to artificially boost your rating, you will be set as a cheater.
Finally, if you receive assistance from someone with you using an engine or better than you at chess, this will be detected and you will be set as a cheater.
If none of these have occurred, and you are still locked at 1500, it's probably because you are playing casual games. Only rated games can affect your rating.