"Which" refers to what precedes it, i.e. "ease". Theoretically, it could refer to the entire phrase "the mobile and the internet infrastructure that existed and the ease". Having it refer to that would not be grammatically incorrect, but it would be unclear.
There are two clauses, both dependent, here: "that existed" and "which customers were able to access technology". This is actually a sentence fragment, not a sentence, because both of the verbs are in subordinate clauses. The entire phrase "the mobile and the internet infrastructure that existed" functions as a noun, as does "the ease with which customers were able to access technology". So this quote consists simply of two nouns connected with "and" and no main verb.