Ok - its a mixture of news. You or your Solicitor should have asked. The council may well argue that by buying the property you accepted the terms and conditions of it, which includes the charges.
However you could write to the Chief Officer of the Council and make a formal complaint. That department will investigate the matter for you and decide whether to uphold it or not.
If they do not, then you can complain to the Local Government Ombudsman. They consider complaints from Councils, offer a free, independent service. Their website is: www.lgo.org.uk
Or you can consider a Judicial Review. This is where the Court reviews the decision of the Council and sees whether it is legal and reasonable.
A Court can either agree with the decision or send it back to the Council to consider again.
More information about Judicial Review can be found here:
Can I clarify anything for you about this today please?