I recently paid off a *-year small loan with my local bank, having never missed a singl...

I recently paid off a *-year small loan with my local bank, having never missed a single payment. I was expecting a boost in my credit score, taking me into “good” range. Instead, I dropped ** points into “poor” credit range. I stopped to talk to the manager at the bank and they said that shouldn’t have happened because I fulfilled my commitment to repaying the loan without issue and they were satisfied with the result. They said they reported the loan paid in full to the credit agency, and that I should not have experienced a credit score drop... let alone a drop into bad credit range. I worked hard towards this and was counting on the better credit score to help with a few things I am about to need for the future. Any help here would be appreciated, thank you.