Buying advice

Hi guys thanks for reading.

We are in the process of buying our first home, but it seems we're stalling at almost every stage.

Our side is all done, conveyancing complete, we are just waiting to agree a completion date and we want to try and exchange before Christmas.

But we can't exchange until the other side is complete, and it seems they have been waiting for a drainage/water certificate for weeks/months.

With the Christmas period coming, and offices closed for weeks, im worried this is all now at risk, FYI our mortgage offer expires at the beginning of February.

Ive spoken to our solicitors, the estate agent and the seller, but it seems theres absolutely nothing we can do and the fact this certificate hasn't appeared yet makes me think it never will.

Does anyone have any advice?