Can I use xlear nasal spray whilst I am using beconase steroid nasal spray. Am suffering chronic sinusitis due to concha bullosa : (?

Yes. Beconase (beclomethasone) is an intranasal steroid to suppress the inflammation in your nose and the xlear is likely a decongestant. Are you seeing an ent? If not, you might want to get those concha bullosas removed or at least consider balloon angioplasty. I would also recommend increasing the Beconase (beclomethasone) to 2 sprays to each nostril twice daily for 2 weeks.
See an ENT doctor. Yes, you can use both, but chronic sinusitis which is producing significant symptoms should be examined by an ENT doctor to be sure you would not benefit from some form of surgical intervention.