Remortgage for lease extension---is this normal?!

lama_pdx

Hi everyone, 
I live in a shared-ownership property and have just obtained an additional mortgage of £6000 to do a lease extension.  (82 years left on lease.)
I received a schedule of charges from my Housing Association landlord, got a quote from my solicitor, found out the premium, everything added up, mortgage approved, all solicitors instructed, all good. I had to pay up front for the valuation but all other fees/charges will be paid upon completion when mortgage funds released. I got all this in writing.

So then suddenly last night I got an email from Housing Association saying I now owe them a Notice of Mortgage charge of £150. What? I sent back to them the schedule of fees they gave me in July and asked why I was now hearing of an extra charge. No response. A little annoying but okay.

Then this morning got an email from my sols, saying that the landlord's sols had asked them to make an undertaking to pay landlord's legal fees in case we don't complete.  So my sols need £900 from me on account before we proceed. 

I just wrote back copying all parties saying I don't have £900 and that was why I got a mortgage. I mentioned the extra Notice of Mortgage fee also and I asked all parties to confirm in writing what monies would be due when so I could liaise with my lender. 

Is this normal? I could in fact sell an investment and pay £900 now but this seems weird and dodgy. 

lama_pdx

On consideration I just sent a screenshot of my sol's email to her over her firm's messaging app and asked whether the email was genuine.