Apparently, the reason you didn't receive that first 5071-C (not 5017-C) because you moved after filing what was then your last tax return filed, which had that old address on it. You got the letter for the 2018 taxes because your 2018 tax return had your new address on it.
"my transcripts came to my old address."
Apparently, the left hand isn't talking to the right hand at the IRS - at least not in a timely manner. You should submit a change of address form to the IRS, as that will ensure it's updated with all departments within the IRS, in a more timely manner. Start at https://www.irs.gov/taxtopics/tc157 for how to do this and get the form.
