It depends on the degree of certainty. The first is less sure, so it could be 8 times, but it's quite a lot. The second is more certain so it's 10 or more IMO.
I hear hyperbole. I think you asking about a case where someone has called someone else over and over to the exasperation of the speaker. I'd say that "must have" is usual there in my dialect (Middle Atlantic, USA) if the emphasis is on the exasperation. If the emphasis is on the number of calls, "probably" becomes more likely.