Billed for an expired contract

My contract ended on the 20 April 2015.. I duly gave 30 days cancellation notice on the 20 March 2015. <br> <br> On the 20 April the line was suspended and I could not make any calls which was fine as this was what was expected and agreed. <br> <br> To my surprise I have been billed R548 this morning for a phone that only received incoming calls. So Virgin please explain how you got to this amount. <br> <br> I am glad that my contract is over as being charged over R500 every month for hardly calling is ripping the consumer off. I am now with Vodacom for 3 months and my bill is never more than R200 and I seem to be calling more than before. <br> <br> I want my money back