"Ο θείος μου έχει μπλοκάρει τις διαφημίσεις."
Translation:My uncle has blocked the advertisements.
"advert(s)" is a valid short term for "advertisement(s)" everybody uses and should be accepted as an alternate, real life translation I believe.
Exactly, and so is "ad(s)". You can also find both of these abbreviations in the Oxford Dictionaries. They should both be accepted.
and to talk about ads generally, you would leave out the definite article in English. my uncle has blocked ads.