I'd start from square one...wires, connectors, the y-connector on the esc rx channel...making certain of continuity. The ESC's signal line on the RX connector might be a place to look for a fault. Motor connectors too. Check for cold-solder joint...or a bad solder due to overheating.

If the problem persists, switch out the esc's into another motor.

Also, the ESC programming beeps may be online. The amnufacturer unknown you might search for a generic progamming pattern.

I'd plug the esc's into a battery one at a time, first to listen for cell count. Then power the ESC off, tx to full throttle power it back on. Listen for a long while, for the pattern(s). When they repeat you have an idea of the set mode. Usually the parameters are brake on/off, then maybe battery type nicad/lipo, then maybe soft start, then maybe timing, bit rate, etc.

For a cheapy generic, there are probably just three, batt type/brake/cutoff type