I have a chip cellular antenna from Pulse W3544B. In the datasheet it is said to make the transmission line 1.34 mm thick which I feel is too huge and also I wanted to make a strip line for impedance matching and according to online calculations the thickness of the strip line is determined according to my dielectric and layer properties. I got 0.325mm. I'm confused which to use?
The width of the stripline is not a design target in itself.
You design a transmission line to have a specific impedance, to match the antenna or whatever is at the other end of the transmission line (or both, if possible).
So, you're right to calculate based on your actual substrate and copper properties. Both 1.3 and 0.3 mm are feasible widths, and variations on a scale of 4 really don't surprise me – there's a large difference in dielectric constants across different board substrates, and a large difference of board thicknesses.
So, make sure you read the datasheet correctly – I can't find your 1.34 mm anywhere in that datasheet, but a clear labeling that says "50 Ω transmission line".
Both the value you calculated and the one stated in the datasheet are feasible, but you have to remember that the value stated in the datasheet represents what fits to the specific user case they have shown.
You are correct in calculating the value yourself, as that is the only method that will give you a certain line impedance value.
Check the datasheet for the impedance required, and run the calculations based on that. If you budget allows for it use the Polar Instrument tools, otherwise, just do like most of us and use the Saturn PCB Toolkit which is free and does the job quite well.