Threatened with Legal Actions After Account Termination

I am being harassed with numerous SMSs by this company to pay an outstanding amount after I cancelled contract with them. I wrote to hello Peter after incorrectly billed for a tracker, they rep**** that a credit note has been issued and also confirmed via email that my services are terminated but after that I still get messages to pay and the amount keeps going up, I don't know what that is for because I close my account with them as they kept debiting me twice. This company will even call to sell their added services claiming that it is to enhance your car tracking device but thereafter you will start seeing double debit orders and when you call they can't explain. I requested that my contact be terminated and they keep threatening me with legal actions from their collections department after they confirmed that my services are terminated? People please be careful when choosing a tracker for your vehicle this company will mess up your credit score unnecessarily as they will list you for nothing when they are the ones who cannot manage small accounts. I am now going to involve my attorneys on such a trivial matter to resolve this ongoing issues with this horrible service experience as this company does not bother to take accountability to resolve it.