I was overcharged when change to my new debit card information and now I cannot cancel my plan subcription plan

I subcribed teacher & student (one-year-plan) and I have been using over 1 year now, on 5th December I changed my credit card information to my new debit card and I was overcharged with the same fees as the plan, and then on 23th December I got charge again which is supposely every month with the correct renewal date.  So the point is this month I got charged twice and it is not acceptable, I would like to refund back to my bank account.  And now I want to cancel my subcription plan I cannot see the botton "cancel plan", and I tried to contact the support team with no answer as well in chat and phone.  Please can you help me to solve my problem here, it is very important and I don't want to waste any unimportant money again.