Tax on saving interest. Tele agent giving misinformation???

Hi, my mother has had her tax code changed for 25/26 to recoup owed interest for savings interest of £264 from 24/25. She earned £20,000 last tax year and will have personal pension income this tax year of £12,570. Surly she has £1,000 allowance for last year and £5,000 this year? The tele agent she called to fix this told her that as she was not a tax payer that the tax reclaim in her tax code was correct. Am I losing my mind or was the tax agent clueless.

Hi,
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