Mortgage refinancing question

For the past ten years I have been paying off a mortgage with Prestia (former Citibank) at a fixed interest rate. The ten year period will end soon. My assumption was that at the end of the term, fixed-rate loans automatically switch to variable unless the customer chooses fixed again (at a higher rate). Prestia has told me "No. If you currently have a fixed rate, you may not switch to variable."
True or BS? From what I have read about other banks, it is the opposite of common practice.

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