I cancelled my contract within the 14 day window but I am still getting invoices

Good afternoon,

I received my SIM card on January 31st 2023 but then canceled my mobile contract on February 7th 2023. I received an email confirming the cancellation but it stated that my contact would end on February 7th 2024. This is a mistake because I canceled within the 14 day window so my contact should have ended on February 7th 2023. 
 

I have been calling for months but no one has helped me cancel the contact and I am still getting invoices even though I am not using the SIM card. 
 

I went into the store for help but they were unable to help me. They logged a complaint on my behalf but no one ended up calling me to resolve this. 
 

After my visit to the store, I received a letter stating the contact was canceled and that I would be refund if I pay the outstanding amount. I paid the amount but my contract has not been canceled, I have not been refunded and I am still getting invoices. 
 

Please help, I am desperate to get this resolved and am loosing sleep over it. 
 

All the best