Good question. In these cases en preemptively replaces the de + noun phrase.

Thus it refers to « de la neige » in the first case and « [des renseignements] sur les crédits » in the second. (I’m filling in « des renseignements » because you couldn’t use en to replace sur + noun.)

But why say those things twice? Well… I see this as one of those nebulous things that makes French more “French”.

The first appearance in the form of en feels natural. It allows « Vous en avez assez » and « Apprenez-en » to sound “complete”. Without en, those phrases are somehow begging for something to fill a syntactic slot that, logically, seems like it could go unfilled.

The second appearance tells you what you’re actually talking about.

So you might say the first one answers a pragmatic/stylistic need and the second a semantic need.

This is a behaviour of en that’s worthwhile getting used to, because it happens a lot. It aligns with other patterns where French likes to both fill a syntactic slot with a clitic pronoun and add the “full version” of the antecedent. In theory there should be a comma somewhere in there, but in the sentences you quote it would break up the flow their advertising copy demands.

Il s’y rend très souvent, à Londres.