Story highlights When some T-Mobile customers call 911, their phones spontaneously generate multiple calls, Dallas city officials said

City officials say the problem has been going on since November

(CNN) Calls to 911 from T-Mobile phones in Dallas are clogging the city's emergency dispatch system, the city said -- and a 6-month-old boy's mother blames the problem for her child's death.

City officials have said that since November some T-Mobile customers who have dialed 911 have inadvertently been making additional calls to the emergency number, rather than a single call.

After T-Mobile crews worked on the problem this week in Dallas, authorities said that abandoned calls -- where it seems like callers are hanging up before reaching 911 -- were overwhelming operators.

A dozen additional operators will be working at the Dallas emergency call center beginning this weekend, according to a statement from the city.

Police are still investigating whether the issue led to the death of Brandon Alex on Saturday. His babysitter said that she dialed 911 multiple times without getting an answer. The 911 operators returned each of the babysitter's calls but could not reach her, city officials said.

Read More