Midland Funding LLC Harassing phone calls for debt that TMobile claimed after I quit the service and was told differently prior to quitting San Diego California

Two and half years ago I quit TMobile after being told my bill was going to be a certain amount.  After I quit I received a bill that tripled the charges that I was told it would be prior to quitting.  I paid what I should have been charged and refused to be bullied to pay charges I shouldn't have been charged.  This fall sometime T Mobile sold the debt to Midland Funding LLC, a collections agency.  They have been harassing me with unidentified phone calls on my cell phone.  I changed my cell number and they found me again.  They put  a claim for the debt against my credit report, too.

Lois, Roseville, CA