Please tell me, could a root canal be filled instead of crowned?

Confusion: You are confused about two different procedures. Root canal therapy is one procedure. Placing a crown on a tooth is a different procedure. Since it is difficult to determine, over the internet, exactly what your problem is, have your dentist explain to you in detail what treatment you need.

After RCT: If i understand your question correctly.... A tooth that has undergone root canal therapy can have a filling instead of being crowned. However, in almost all cases, the crown is preferable as it better protects the tooth against further decay and breakage. It's a good investment after the expense of the rct. Your own dentist can better discuss your options and risk\reward of a filling vs a crown.