fix(ramp): use hexToBN for ContractBalances balance

[wachunei]

Description

This PR fixes a missing line to convert to BN instance from this previous PR

Related issues

Fixes:

Manual testing steps

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Screenshots/Recordings

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[tommasini]

LGTM! If possible just see if the cast could be to Hex! Or better, type the return of this function as Hex at the utils folder

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
12.5% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud