Waiting for a written offer

I received a verbal offer from HSBC in the first week of August. I was told up front that the process for the written offer would take 4-6 weeks.

6 weeks passed and I didn’t receive a written offer. During those 6 weeks I met with the VP I interviewed with in-person and he said I shouldn’t get nervous since it takes time at HSBC due to the approval processing going through London. He mentioned it took nearly 3 months for him (but the reason for the delay on his offer was in regards to his 401k at his previous job).

I left the country for vacation back in late September and had one last communication with HR before I left where in I was told the following: “The offer approval remains in process, and we have not been given an outlook on when it will be approved. [Group Head], and his manager, have continued to flag this offer as a critical hire to complete. We will let you know when we receive any further update.” In addition, I was told to touch base once I came back to the States.

I came back last Thursday and called and emailed HR on Friday but didn’t receive a response. Should I be getting worried?