Qiàn le qián jiù děi huánzhài, zhè shì tiānjīng-dìyì de shì.
If you owe money, you have to pay it back; that's only right.
Tips
grammar
还 here is pronounced huán (2nd tone, to return), not hái (still/yet). 还债 is a verb-object compound, so you can insert things: 还清了债 (paid off the debt completely).
