You need to be completely clear with CS what your real problem is, don't bombard them with issues.

The expensive item will have to be dealt with under the money back guarantee, if necessary.  I suggest you don't talk to them about that because they can't help at this point.  The same goes for the cheaper item, you will either get it or you won't,  and the money back guarantee will cover non receipt.

Ebay won't do anything about the messages.

Which leaves your suspicion that your account has been hacked. They can help you secure that.