Old unknown invoice discounted from rent

Letting Agents

I have my property rented with Countrywide. Last year the old tenants left and we stated a new contract with new tenants. At the end of the old contract there was no mention of any unpaid invoices. However this month Countrywide discounted directly from the monthly statement a very large invoice from 2018 (old contract) which is related to works I didn't know anything about nor have agreed upon. Is it legal to force an invoice from the past upon the landlords? Are they allowed to help themselves with money from my management account directly without consult with me ? How can I protect myself against such type of abuse from the letting company?