1. Doing it for free might be a difficult process but i'm lacking some information about the specifics of they type of distortion/compression issue you are facing audacity is a great audio editing tool and has a repair function alongside many other functions based on the type of quality distortion the harmonics might be able to be detected though noise detection and removal inside of audacity,

2. however if you are looking for an alternative paid software
Izotope RX8  is a wonderful professional paid tool to separate vocals and or instruments from music they also have deals from time to time and is a solid choice for many professional audio needs

3. if neither of those options help you if you describe the type of quality distortion you need if it is no distortion and just is low quality you might be able to fix this audio using some effects of supersampling. Creative audio labs company has a signature crystallizer effect that is designed to take lower quality samples and make them into higher quality samples, however for this method you may need some sort of external recording device.

let me know if you need more information about any of these or to try something else.
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