Translation brings to light all the odd things about language.
In Latin America, “No” is used as a general interjection like “oh” or “um”, often combined with “pues,” another interjection that has little meaning. A sentence that starts with “No, pues, es que estuvimos…” might be be translated as “Oh, well, we were…” or “Yes, but the thing is that we were…” or “No, because we were…” depending on context.
One of the oddest Spanish concatenations is the expression “No, pues sí,” which literally means “No, well, yes”:
“¿Pasaste por la tienda?”
“No, pues sí, pero no había de eso.”
“Did you go to the store?”
“Oh, yeah, but they didn’t have any.”
We English speakers all know that a week has seven days, so two weeks is 14 days, three weeks is 21, and so on. In Spanish, however, “ocho días” (eight days) to refers to a period of week. A week from today is “en ocho días” because today and next Wednesday both get counted. Two weeks is “quince días” (15 days) by the same principle.
When you get to three weeks, however, things get tricky. In Costa Rica it’s “veintidós días” (22 days) but in Colombia it’s “veinte días” (20 days).
However… four weeks is not “29 días”. It’s “cuatro semanas” (four weeks) or “treinta días” (30 days), either of which may refer either to the same day of the month (the 18th of July) or the same day of the week (Wednesday four weeks from now). Dates that far out are likely to be fuzzy in any case, so your best bet is to check a few days before to find out when you are expected (or if they even remember that you had an appointment).