Sounds like Sinktel.
Sinktel Operator: No sir, you cant reactivate your mobile line
as there is an outstanding charge on your account.
Me: I don't owe you any money.
Sinktel Operator: There is an outstanding of $250
Me: No, are you checking the correct account?
Sinktel Operator: You defaulted on payment for your ADSL
line.
Me: What nonsense! I owe Sinktel $0. Tell me which month was the
$250 for.
Sinktel Operator: It was an early termination charge for your
ADSL.
Me: You are supposed to REACTIVATE my ADSL the last time, and
also waive off any charges because the fools in Sinktel
lost my change of billing address letter. I submitted the
changes for my change of billing address for my ADSL line and my
mobile TOGETHER. I did not receive my bill because your idiots at
Sinktel failed. When the last time they called me, I had already
told them over the phone to reactivate the ADSL line and also paid
the outstanding even though they did not bill to my new house. I
even had them promise to update my billing address for my ADSL.
Tell me what is my billing address on your screen.
Sinktel Operator: *mumbles old billing address*.
Me: It is still the FREAKING OLD ADDRESS. It is Sinktel's fault,
so rectify the problem and reactivate my mobile now.
Sinktel Operator: You have to call the billing department during
office hour so that they can check into this issue.
Me: I call them with WHAT? I owe Sinktel $0 and they cannot
reactivate my mobile line, and STILL NEED me to call them during
office hours? I work in a call centre and CANNOT call you during
office hours.
Note: Many godzillion years ago.
The outcome of the story? I terminated my mobile and ADSL.

My hubby experienced something similar with his handphone but it
was with M1