Failure to credit account as promised

I previously logged a complaint regarding a billing error whereby I was being charged for calls from a line that did not belong to me. I was contacted by Eric from the social media team who promised to resolve the issue by disconnecting the line and then crediting my account. The line has now been disconnected but I am yet to be credited for the amount that were incorrectly charged to me. I have sent numerous emails to the social media team but have been ignored. I have also given up trying to call the customer care line as the agents do not understand my query and continuously transfer my call to different departments with no resolution. My reference was SM136616.