Both sentences are grammatical, but they mean different things. While sentence 1 is sure about the number of times the request was made, our sentence 2 approximates the number of times "I had to tell him" in order to get the same result. They are not saying the opposite, it is only the degree of certainty that differs.

Must, may, might, can’t and couldn’t are used with a present perfect verb form to show how certain a speaker is that a past situation happened or didn’t happen.

Formula: MODAL + HAVE + PAST PARTICIPLE (to show how certain the speaker is that something happened)

Must have + past participle shows a great deal of certainty that something happened, but there is still some doubt in the speaker’s mind. He/she is not 100% certain. For example:

• The students did well on the test. They must have studied hard.

(University of Victoria, Canada)

Both sentences are grammatical, but they mean different things. While sentence 1 is sure about the number of times the request was made, your sentence 2 approximates the number of times "I had to tell him" in order to get the same result. The two sentences are not saying the opposite, it is only the degree of certainty that differs.

Must, may, might, can’t and couldn’t are used with a present perfect verb form to show how certain a speaker is that a past situation happened or didn’t happen.

Formula: MODAL + HAVE + PAST PARTICIPLE (to show how certain the speaker is that something happened)

Must have + past participle shows a great deal of certainty that something happened, but there is still some doubt in the speaker’s mind. He/she is not 100% certain. For example:

• The students did well on the test. They must have studied hard.

(University of Victoria, Canada)

Both sentences are grammatical, but they mean different things. While sentence 1 is sure about the number of times the request was made, our sentence 2 approximates the number of times "I had to tell him" in order to get the same result. They are not saying the opposite, it is only the degree of certainty that differs.

Must, may, might, can’t and couldn’t are used with a present perfect verb form to show how certain a speaker is that a past situation happened or didn’t happen.

Formula: MODAL + HAVE + PAST PARTICIPLE (to show how certain the speaker is that something happened)

Must have + past participle shows a great deal of certainty that something happened, but there is still some doubt in the speaker’s mind. He/she is not 100% certain. For example:

• The students did well on the test. They must have studied hard. (source)

Both sentences are grammatical, but they mean different things. While sentence 1 is sure about the number of times the request was made, our sentence 2 approximates the number of times "I had to tell him" in order to get the same result. They are not saying the opposite, it is only the degree of certainty that differs.

Must, may, might, can’t and couldn’t are used with a present perfect verb form to show how certain a speaker is that a past situation happened or didn’t happen.

Formula: MODAL + HAVE + PAST PARTICIPLE (to show how certain the speaker is that something happened)

Must have + past participle shows a great deal of certainty that something happened, but there is still some doubt in the speaker’s mind. He/she is not 100% certain. For example:

• The students did well on the test. They must have studied hard.

(University of Victoria, Canada)