HR being unreasonable[N/A]

Hi all! My company(Canada,Ontario) has a work from anywhere for a maximum of 6 weeks in a year. I recently used this policy for my travel earlier this year for my marriage. No here's the catch we have to submit an approval to leverage this policy and I did. The mistake I made was this : I had to travel for 6 weeks out of which I need work from anywhere only for 3 weeks and the rest 3 weeks were PTO. On the form I accidentally mentioned that I need work from anywhere for the entire 6 weeks without being unaware that my PTO will also be counted towards the Work from anywhere allotment.

Now I have to make an urgent travel for an extremely important purpose and only while making that request, I ealised that I have used my allowance for the whole year. I am trying to figure out a way with the Hr if they are able to accomodate my request and give me the rest 3 weeks of credit that I owe which stemed out of misunderstanding.

The HR has been really uncooperative so far however, my managers are aligned and supportive of my travel request.

please help if someone has good advise to navigate this situation.