Major issues with Opencart Version 1.5.1.3, HELP!

I have built an online store for a client using Opencart Version 1.5.1.3.

Firstly, we're having major problems with orders going through as abandoned. I have looked into a bunch of posts here regarding this, but nothing seems to help. I had been using this server with another Opencart store in the past with no issues what so ever. Now, all orders go through to abandoned, it's so frustrating, how can I fix this huge issue?

Also, another major problem is that some of the customer payments have been going INTO SOMEONE ELSES PAYPAL ACCOUNT! I have checked the email and PDT token, and it's the correct details. Also, on top of this, one of the customers received a message, sent from the admin section of Opencart saying this

Hi Claire,

Good Day! We are having a PayPal issues regarding on the payments you sent. The item is in already shipped and we would like to have your patience to wait and help us on solving regarding on the paypal payments. We recommend you parcipate on it.

Thank you!
Customer Service

This was not sent by anyone who has access to this shop! It seems to be someone who does not speak good English.

Are we being hacked? What should I do to fix all these issues?

The site has SSL.

Please help, thanks.

I'd say. Looks like it's time to house clean for you.

Thanks for the response, but what exactly do you mean by house clean?

Have you enabled debug mode on PayPal within OpenCart? This will send all the PayPal details to the error log and you can see exactly what is happening with the payment