You could tell him politely you are finding it difficult to understand him & could he speak & little slower & clearly, i had same problem with tech support in India but i did that & got the problem sorted without offence, & because rather than get upset & slowed it down she actually surprised me by thanking me for 'my' patience which was nice to have understanding on both sides & was pleasant

I presumed she had that problem a lot. I suppose if it is that bad im sure you could ask, as have spoken to sky myself at least once a month, there have been some strong scottish accents, i suppose im getting used to it LOL!!!