1. Lock your bank account immediately.
2. Call Sony, if they won't reverse the charges, then you do step 3. If it happened today, then forget this and just call your bank. The time you call and where you are located are good details for the bank to know since they can find out where the actual transaction occurred. Especially when you call on the day of when the unauthorized transaction occurred.
3. Call your bank and file a claim. The reason why you should do step 2 first is because the bank will ask you if you called Sony to see if they were willing to help. Since you're filing the claim, you will just tell them Sony wasn't going to cooperate with you.
4. Wait patiently.
The bank will give your money back temporary until the investigation is finished, so remember not to use it until it's official.
5. Get your PSN account back if not done so already and starting using prepaid PSN cards.
Someone used by debit card number online and bought something from Toys R Us in Philly while I was in Tampa. Dunno how this happen since it's been couple of years since I used by debit card, but after waiting awhile, I was able to get my $50 back. So you shouldn't have a problem get your $70 back.
Just stay confident and don't lie. If Sony doesn't cooperate with your bank, then there is a good chance of the bank favoring you.
Btw, I have Bank of America, but the process should be similar for all banks.