You have a problem There are limited resources on a microcontroller. Get an Arduino that has more timers (if you currently use an Uno/Nano/Mini, 32U4 based or a Mega provide extra timers).
Or use something else instead of the tone library; switching a pin on and off at a certain 'rate' gives you a tone. An extremely simple example
void loop()
{
 digitalWrite(tonePin, LOW);
 delay(10);
 digitalWrite(tonePin, HIGH);
 delay(10);
}
gives a tone of roughly 50 Hz. There are limitations to this (even if you use a millis / micros based approach) so your mileage will vary