"US companies" like Lewis, Bajabound etc, selling "Mexican" insurance, are brokers for 3 or 4 Mexican companies. Normally, those Mex companies cover legal fees.
When in accident, you call Mex toll-free number provided by the policy. Some gringos are calling office number of the US broker - you won't find it on the policy, they are just a broker, so it's better to write it down when buying. I don't know why I would need the US broker number in Mexico, but I would imagine it being useful when dealing with claim repairs North of the border. It has to go first through Mex adjuster anyway.