I've seen some cases like
"He want back to working"
"He decided returned to playing soccer"
"Mexico went from exporting just coffee and oil to exporting: cars, tv, engines, laptops, etc.
Why ?
English teachers always say there are to options "to-infinitive" and gerund but I have never heard about a gerund with "to" before
It's not a "to gerund". "To" is the preposition used with the verbs "go back", "return" and "go" to denote the destination (real or metaphorical). This "to" cannot be followed by an infinitive, so a following verb must be gerund.
Note the difference between:
He went to see his friend.
"To" introduces a purpose clause, and takes the infinitive.
and
He went back to stealing.
"To" introduces the destination of the (metaphorical) journey, and cannot be followed by an infinitive.
