The customer should always transact with these companies in writing.
You could have supplied at least an email to company narrating your representation at two offices of company.
You may log on to website of company obtain eamils and escalate your matter to MD,Company Secretary and conclude deficiency in service of the comapny and express that you shall only upto month you visited Airtel after shifting to new city provided comapnies submit new bill to you in which all penalties are waived off and submits a letter that company has also withdrawn your name from all collection,recovery agencies, list of defaulters visible to all companies, credit rating agencies, credit bureaus etc.
You can also mention that you are prohibitibg the company and its agents to make any phone call at any of your phone numbers and if company wants to meet company may submit an application seeking appointment from you and after the meeting company employee shall have to submit minutes of discussion in writing in original then and there.
The employees in this company are unwilling to accept their lapse and deficiency and hence happy to refer to recovery agents to save their skin.
If recovery agent misbehaves you can lodge a police complaint.
Later you can also approach Lok Adalat,DCDRF.