CARTRACK DEMANDING EXTRA PAYMENTS

I changed bank accounts 4 months ago and have been paying my Cartrack directly to them (for the past 4 months). On Sunday I received both an sms and email from them to say my deduction failed and that I am in breach of my contract with them.I immediately rep**** to the email,attaching proof of payment. On Monday I also received a whatsapp message from them,still with my account being in arrears. I rep****,also sending proof of payment and then yesterday received yet ANOTHER whatsapp message wanting to claim payment. Up till now no one from Cartrack has tried to contact me to clear this up or to apologise to me. Someone on whatsapp just sent a "thanks" after I sent proof of payment,but their client services and accounts department need to be looked at,also their lack of professionalism.