@ Avleen Kochar
1. you can wear ruby and yellow sapphire together now too.
2. Wearing Ruby only may or may not have had any bad effects when you were asked to wear both.
All depends on what was the need or problem for which the advise was given, matters also depend on your horoscope and the running periods and transits of that time and the present time.
I cannot irresponsibly advise you without knowing your horoscope and problems.
Wishing you good luck, May God bless you and above all?????
CHEERS