You should challenge that! if you had a 40 year mortgage and 5 years has past, you are able to renew at 35 years provided your are not making any changes to the mortgage. If you ask to increase the mortgage, then a max 25 year amortization would apply.
If you don't get the answer you are looking for, considering transferring the mortgage to another lender. I just did that for one client, and the other lender kept the same amortization in place at 32 years. Straight transfer, no new money, 87% ltv on a rental property.