Hi! I agree with John: 1) “Bob hasn’t called me since last week” means he called you last week but hasn’t called you this week - there is no definite time period. 2) “Bob hasn’t called me for the week” means that he hasn’t called you for a specific time period - the week. By the way, instead of 2) I would say “Bob hasn’t called me in a week”! Isn’t English fun?!:D

Since last week = bob phoned you in the previous week, he has not phoned you during this week, the current week. For the last week= bob has not phoned you during the last week (seven days). The way this is used may vary a little depending on how individual people count or consider each week. If it is Monday at a workplace and work time is Monday to Friday. Some people may say "bob hasn't phoned me since last week. On any day from the current Monday to Friday working week. Because before the previous Sunday they would consider it as last week. Some people may in their head count the individual days and say on a Monday bob hasn't phone me since/for a week, counting back to the previous two Sundays or previous Monday. So basically people either count back Seven days or they count back to when they personally consider each week to start. Which could be typically Friday, Saturday, Sunday or a Monday. You are correct grammatically in your understanding of since and for. This is what what you must learn for the classroom and for English tests/exams. However you need to be aware of the different ways people use the two structures often interchanging them to mean the same. Also adding in extra words like in/over/during/ the last week. There are two ways that are considered for language learning one is to be obsessed with grammar and linguistics, and other people and teachers think that just communicating is what language should be about, but in reality it's a mixture of both. In a real life situation whether you hear since or for just know they are referring to one week either seven days or a working week that to them may begin earlier or later than the week you imagine in your head. When does a week start or end?

Thank you very much dear Sylvia. I really appreciate you answering me :))

One difficult thing about English is that there are always different, informal variations on standard rules. Many of these variations evolve in different geographic locations - and if they are extremely different with regard to pronunciation or idiomatic English, they evolve into local dialects. Geordie and cockney dialects in England are an example of this. Your question is one of grammar though , and it's a great question. As a native speaker, I would never say ' Bob hasn't called me for the last week'. I might say 'Bob hasn't called me IN the last week'. But, really, you are correct in your knowledge of standard English rules for 'since and for' . As a language learner you can't go far wrong if you follow standard rules of grammar - such as for/since above. Some speakers say 'in the last week' - to specify which week they are talking about, but that's not necessary when it's much easier and clearer to 'since last week'.