Comma required or not

Solution 1:

There is no need for a comma in this sentence. However, the section from 'I received..." onward is not an independent sentence; in fact, "the laptop repair service I received from your service center" is a noun phrase, so there is no benefit to putting a comma in to break it up. You could say 'that I received', or (better in my opinion) 'which I received...', but sentence 1 as it stands (with the addition of the final r on 'your') is perfectly intelligible.

And I'd definitely say 'dissatisfaction with...'

With my editor's hat on, I might suggest recasting the sentence to make it pithier:

"I am writing this letter to express my dissatisfaction. Recently, I took my laptop in to your service centre..."

But that's style, not grammar.