In mainland China, we don't have this usage. 

I have checked on internet, and find out that  西北 is also a spoken word in Taiwanese which means very much.

A Malaysian word which means 'very much' sounds like '西北', so she  just uses ‘西北’ to instead of the Malaysian word.

The sentense means ‘really miss you very much’

普通话/华语 (Mandarin) is a main Chinese unifying language, but there's many dialects originating from China. For example, the people of Guang Zhou (China) mainly speaks 广东话（Cantonese）and the people in Fu Jian (China) mainly speaks 福建话（Hokkien）. Many Chinese in the 1900s traveled down Asia and had set their foots on several land and so, countries like Hong Kong has people speaking Cantonese and in Taiwan, people speak Hokkien.

So to answer your question, many Chinese also traveled down to Malaysia and Singapore where they brought their dialects along. 

The lyric states, '真的西北西北好想你'.  The  '西北(Sibei)' referred here is spoken in Hokkien. When it's translated to Mandarin, it is 非常 (Very).

Joyce Chu's from Malaysia, and it's very common for Malaysians to mix Bahasa Malay, Mandarin, Cantonese, Hokkien and Malay in one sentence. In the lyrics stated above, Hokkien and Mandarin was used to form a sentence. 

Hope it helps!

- A Singaporean who uses Singlish/The mix (rojak) of languages as well

It's a misspelling word of Teochew which is a Chinese dialect.They just used the wrong spelling

It should be 死父(si2 be6),which means very much.And this word is kind of rude,so this sentense can be "f*cking miss you"