Run 2 Motors on 1 Speed Controller (ESC)

Hi everyone, having a bit of an issue with my new FW robot. I built it to be 4wd, each wheel with it's own motor. I rigged up a speed controller to each side - 1 speed controller running two motors. All sounds promising until I ran the bot... then pop and smoke from a motor. So reduced voltage to see if there was too much voltage (6s down to 4s). Speed controllers supposed to be rated up to 6s... Guess what when run again, same on other side and could only run forward not backwards. These controllers are Chinese cheapo's but should have been capable of running the motors, I believe. The motors by the way are 12 to 24v 30w 3000 to 6000 rpm brushed.
I know there are going to be many questions, but asking if anyone else has had similar problems and how they overcome them also what do people use for there 4wd brushed motors?
Thanks for reading.

There are a lot of cheap ESC's for cars that don't run backwards. or with reduced capabilities.

And for Brushedd motors in Feathers, we started with the Robot Power products, at first the sidewinder, later on the Scorpion XXL Ilyama version, but went to the IBF 4.5 a few years ago.

Even if the ESC's can handle the 6s Voltage, how about the Ampage draw of 2 motors at stall torque? This figure should be listed in the motor's datasheet, doubled (2 motors per esc) and compare to the ESC's stated value.

Hi all, thanks for the advice. Had a look at the esc's they are blown. With further investigation I have found they where sold as 6s compatible however, they are actually 4s.... they also should have had an over voltage protection to them... anyway, motors are still good, so bought a couple of quicrun 880 esc's and running bot on 4s lipo's. So all should be good... fingers crossed.
Later once I've proven bot design after Grantham, I shall upgrade motors, batteries and esc's.
Hope to see you there. Cliff.