Importing tax and B2G form


I moved from the US to Canada a few months back but recently received invoices from FedEx that they had paid duty taxes on my behalf for the personal belongings I shipped from the US to Canada, even though I obtained a stamp at the Canadian border for tax exemption.

Fedex says I need to pay the invoices but I can submit a claim to the CBSA with a B2G form. Has anyone experienced something like this before?