Unfortunately there are no such things as Grandfather Rights in this situation. The new managing agents (as agents for the freeholder) are entitled to ask for payment of service charges in accordance with the terms of the lease. Their justification for asking for an administration charge for payment by standing order will be that such payments involve them in more administration than payments by monthly direct debit. However all is not lost. You can write to them (don't phone) and say that you believe that their administration charge is unreasonable and invite them to withdraw it as you have been paying in this way since 2002. Keep a copy of your letter. If they will not withdraw it, don't pay it, but carry on paying the rest of the service charges. You will accumulate arrears but the freeholder cannot recover such arrears unless a court or the leasehold Valuation Tribunal (LVT) finds that the charges are reasonable.
Talk to others in the block. If they find that the new managing agents are unreasonable, you can collectively form a Right to Manage company and take the management away from the freeholder and his managing agents. Any suggestion that you may be about to do that, may be sufficient to "persuade" the current agents that imposing a charge for payment by standing order is perhaps not such a good idea after all.
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