Has anybody any experience of negative equity trade up?

Been approved for a NE trade up mortgage and will be carrying c.€30k NE once current property is sold. Now at the point of contracts issued for sale on our current property and our solicitor is looking for confirmation from the bank that the bank will release the charge on the property once proceeds are lodged. After 3 weeks waiting on an answer, bank are saying that we need to sign the new sanction letter in order to give this confirmation, but we have yet to find a new property to purchase, so not clear what the repayments will be on the NE element that remains pending drawdown of the new mortgage and cannot get an answer on this from the bank.

Anyone been in this position and how did it fair out??