Signed up with coinbase over a year ago. Had the same issue as you did... tried to add a debit card to my account and wouldn't link it up. Said it was invalid. Customer support is no help. Left them... went to Circle.... when Circle changed their mind about buying and selling... had no other place to go.
Received an odd email from coinbase this month. It said... your bnk account and debit card as been increased MAX. I was like
because I haven't even logged into coinbase in 7 months. Went to add another debit card... and it added it with zero problems.
I think they just love to screw with select accounts. I just don't understand why my limits were increased when I never used them or emailed them in 7 months? Totally odd.