The change of a freeholder should not directly impact your mortgage. The terms of the lease, which is the contract between you (the leaseholder) and the landlord (the freeholder), remain the same even if the freeholder changes. Your obligations to your mortgage lender are also separate from the lease, so your mortgage terms and repayment arrangements should not be affected. However, it's a good idea to inform your mortgage lender about the change of freeholder.
While the terms of the lease itself don't change, the management style or practices of a new freeholder might. For example, they may handle maintenance, repairs, or service charges differently, which could indirectly affect your finances. If you have concerns or face issues following a change of freeholder, you may want to seek legal advice.