You broadband takes their customers granted

I selected a you broadband wifi pack in June 2018 and had paid my money by cheque. Then these people call me and tell me that due to some spelling mistake the cheque is bounced and I hav to pay around 172/- more. I needed wifi urgently so I asked them to come and collect the cash+extra cheque bounce charge. And start the wifi soon. And when the guy from you broadband came to my house I asked him, “in how many days i’ll get my bounced cheque back?” And he quoted “within 7days”. It’s been 2months. No call or no cheque has been received. So I called the guy 10days back and asked him about the cheque and he said today he will bring my cheque back to me. But no. He did not. I called him the next day he said he is out of station so he will bring my cheque in a day or so. But he did not. I have all the bills but they r not giving my cheque back and I think I haven’t made any spelling mistake white writing the cheque and I also think that they will misuse it later. Can you please help with this problem? Thank you in advance