In all probability the problem has probably been created by mucking around with your business policies etc.

Did you manage  to finally  cancel the listing that was initially causing you trouble, listing number has not yet been disclosed here, so we can't offer anymore help there.

Was click & collect  causing the problem, as suggested,

Despite you denying using click & collect,  it was listed as a valid shipping method on well over half your listings.  

Either you have since opted out of  click & collect,  or it was removed from your listings via ebay, the later meaning you were in breach of click and collect terms and subject to penalties and restrictions.

As you have admitted fiddling with your business policies etc, that is where I would be looking to resolve your current issues.