Silence is also a message. You cannot force a reply — what you can do is make your side of the record complete, calm, and impossible to misread.
One message: what is happening, what you need, by when. No preamble about the last silence.
If there is no answer by the time you named, do the reasonable thing and note it: "No reply by Tuesday, so I've arranged the lift." You are not punishing anyone — you are keeping life moving.
Three unanswered messages read like pressure in a record; one clear message with a date reads like a parent organising a child's week.
Log what happened even when nothing was agreed. A one-sided record kept calmly is persuasive; a one-sided argument is not.
Confirmation requests give a silence a shape — asked, seen, unanswered — and the logbook keeps your own account in your own words, dated, without sending anyone anything.