Solicitors want to charge for gift

UK - pending mortgage completion.

Our solicitors have checked my bank statements and found a gift from my parents of £2k, and now they want £75 for "using a gift towards the mortgage" and £20 for an ID check.

The gift was for Christmas has absolutely no relation to the mortgage. Without the £2k our financial situation would have been the same, and the same level of deposit.

Are we within our rights to refuse, or is there any way to declare that this gift was not related to the mortgage?

It seems like money for old rope to me.

Any advice would be appreciated.