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Any score purchased via myFICO.com, as the name suggest, is a FICO score. Specifically, the TU score purchased through here is a TU98 score. If you purchased scores from any other source, including directly from TransUnion, then you do not have a FICO score. Make sure you are comparing apples to apples.
If the CSR from TransUnion told you your score, she did not give a FICO score. TransUnion does not sell FICO scores. They sell a non-FICO score called either a TransRisk score (sold by TrueCredit, CreditKarma, etc.) or a VantageScore. Lenders generally don't use these scores. Ignore them. She was giving you some bad advice.
If you pulled a TU FICO here, from this website, of 608 and then a 583 also from this website, then your score did obviously drop. Why did it drop? Hard to tell from the info you provided, but a dispute can drop your score in certain situations. Also, settling an OC debt could also drop your score. Settling your only unpaid CC, for example, can also drop your score.
What scores did your lender provide? BTW, generally, a 620 mid-score is needed, rather than all 3 being above 620. If 2 of your 3 FICO scores are above 620, then you're likely past that hurtle.