After a 5071C letter, verified my ID with IRS & was told I’d receive my refund in 3-4 weeks. 5 weeks later still no refund. Was told it can take a total of 9 weeks. Why?

When asked if there were problems w/ the electronically filed (TurboTax) return, they couldn’t/wouldn’t answer. Said to call after 9 weeks if no refund or letter in meantime. I was polite, but they acted annoyed/rude to me for asking.