Two different things
Pulsa is phone credit, for calls and texts. Kuota is a data allowance.
They are bought separately and confusing them is the standard foreigner mistake. Topping up pulsa does not give you internet unless you then convert it into a data package.
Mau isi ulang. ‘I want to top up.’
Kuota berapa giga? ‘How many gigabytes?’
Paket data sebulan berapa? ‘How much for a month of data?’
Buying a SIM
Mau beli kartu perdana. ‘I’d like a new SIM card.’
Kartu perdana literally means a maiden card. You will need your passport, and the shop will register it for you, which is a legal requirement rather than a favour.
When it does not work
Sinyalnya jelek. ‘The signal is bad.’
Nggak ada sinyal. ‘No signal.’
Lemot. ‘Slow.’ Casual, from lelet plus lambat, and extremely common.
Wifi nya mati. ‘The wifi is down.’
Mati is worth its own note. It means dead, and it is used for anything switched off or not working: lampu mati ‘the light is off’, listrik mati ‘the power is out’, HP saya mati ‘my phone is dead’.
Passwords and connecting
Kata sandi is password, though almost everyone says password.
Password wifinya apa? ‘What’s the wifi password?’
That sentence will earn its place in your first week.
HP
HP, said ha-pe, is the word for a mobile phone. From “handphone”, which is not English but is universal here.
HP saya ketinggalan. ‘I left my phone behind.’ Note ketinggalan, the casual form of the ter- accidental you met in the affixes chapter.