The following may not constitute sufficient cause for the utility to terminate service to an existing customer: Failure of a previous customer to pay for service at the premises to be served, unless the current or prospective customer is in violation of one of the provisions of Regulation .04 of this chapter; Failure of the customer to pay: For merchandise purchased from the utility; For a public utility service other than electric service, gas service, or electric and gas service, as the case may be; For service that is used in other than dwelling units; The bill of another customer as guarantor of that other customer; A bill which is delinquent for less than 3 months if the security deposit exceeds the amount of the estimated final bill for service; Any outstanding bill which is less than $100, and which is delinquent for less than 3 months; Any undercharge for the period in excess of 4 months as described in COMAR 20.50.04.05 and 20.55.04.05; or An outstanding bill that is over 7 years old, unless the: Customer signed an agreement to pay the outstanding bill before the expiration of this period, or Outstanding bill is for service obtained by the customer in any manner described in COMAR 20.31.02.03D or 20.31.02.04A(1)—(4).